diff --git a/docs/app/experiments/dialog.tsx b/docs/app/experiments/dialog.tsx
index 79dfd39804..c1dd9fe760 100644
--- a/docs/app/experiments/dialog.tsx
+++ b/docs/app/experiments/dialog.tsx
@@ -150,7 +150,7 @@ function ReactSpringDialogDemo({ animated, keepMounted, modal, dismissible }: De
   );
 }
 
-function ReactSpringTransition(props: { open: boolean; children?: React.ReactElement }) {
+function ReactSpringTransition(props: { open: boolean; children?: React.ReactElement<unknown> }) {
   const { open, children } = props;
 
   const api = useSpringRef();
@@ -179,6 +179,7 @@ function ReactSpringTransition(props: { open: boolean; children?: React.ReactEle
   }, [api, open, mounted, setMounted]);
 
   return mounted ? (
+    /* @ts-ignore springAnimated.div props type does not include children and errors in React 19 */
     <springAnimated.div style={springs} className={classes.springWrapper}>
       {children}
     </springAnimated.div>
diff --git a/docs/data/components/tooltip/UnstyledTooltipFollowCursor.js b/docs/data/components/tooltip/UnstyledTooltipFollowCursor.js
index 957eceae5c..1d8e8265a0 100644
--- a/docs/data/components/tooltip/UnstyledTooltipFollowCursor.js
+++ b/docs/data/components/tooltip/UnstyledTooltipFollowCursor.js
@@ -6,7 +6,7 @@ import { styled } from '@mui/system';
 export default function UnstyledTooltipFollowCursor() {
   return (
     <div style={{ display: 'flex', gap: 12 }}>
-      <Tooltip.Root followCursorAxis="both">
+      <Tooltip.Root trackCursorAxis="both">
         <AnchorButton>Anchor</AnchorButton>
         <Tooltip.Positioner sideOffset={5}>
           <TooltipPopup>Tooltip</TooltipPopup>
diff --git a/docs/data/components/tooltip/UnstyledTooltipFollowCursor.tsx b/docs/data/components/tooltip/UnstyledTooltipFollowCursor.tsx
index 957eceae5c..1d8e8265a0 100644
--- a/docs/data/components/tooltip/UnstyledTooltipFollowCursor.tsx
+++ b/docs/data/components/tooltip/UnstyledTooltipFollowCursor.tsx
@@ -6,7 +6,7 @@ import { styled } from '@mui/system';
 export default function UnstyledTooltipFollowCursor() {
   return (
     <div style={{ display: 'flex', gap: 12 }}>
-      <Tooltip.Root followCursorAxis="both">
+      <Tooltip.Root trackCursorAxis="both">
         <AnchorButton>Anchor</AnchorButton>
         <Tooltip.Positioner sideOffset={5}>
           <TooltipPopup>Tooltip</TooltipPopup>
diff --git a/docs/data/components/tooltip/UnstyledTooltipFollowCursor.tsx.preview b/docs/data/components/tooltip/UnstyledTooltipFollowCursor.tsx.preview
index c95cdc12a4..122da4a445 100644
--- a/docs/data/components/tooltip/UnstyledTooltipFollowCursor.tsx.preview
+++ b/docs/data/components/tooltip/UnstyledTooltipFollowCursor.tsx.preview
@@ -1,4 +1,4 @@
-<Tooltip.Root followCursorAxis="both">
+<Tooltip.Root trackCursorAxis="both">
   <AnchorButton>Anchor</AnchorButton>
   <Tooltip.Positioner sideOffset={5}>
     <TooltipPopup>Tooltip</TooltipPopup>
diff --git a/docs/next-env.d.ts b/docs/next-env.d.ts
index 4f11a03dc6..40c3d68096 100644
--- a/docs/next-env.d.ts
+++ b/docs/next-env.d.ts
@@ -2,4 +2,4 @@
 /// <reference types="next/image-types/global" />
 
 // NOTE: This file should not be edited
-// see https://nextjs.org/docs/basic-features/typescript for more information.
+// see https://nextjs.org/docs/app/building-your-application/configuring/typescript for more information.
diff --git a/docs/next.config.mjs b/docs/next.config.mjs
index 97659e6bce..9a24d92526 100644
--- a/docs/next.config.mjs
+++ b/docs/next.config.mjs
@@ -63,6 +63,7 @@ const nextConfig = {
     : {}),
   experimental: {
     esmExternals: true,
+    workerThreads: false,
   },
 };
 
diff --git a/docs/src/blocks/Demo/DemoSourceCopy.tsx b/docs/src/blocks/Demo/DemoSourceCopy.tsx
index 92177f5d6f..e78d1b43ff 100644
--- a/docs/src/blocks/Demo/DemoSourceCopy.tsx
+++ b/docs/src/blocks/Demo/DemoSourceCopy.tsx
@@ -43,6 +43,6 @@ export namespace DemoSourceCopy {
   export interface Props extends React.ButtonHTMLAttributes<HTMLButtonElement> {
     onCopied?: () => void;
     onError?: (error: unknown) => void;
-    render?: React.ReactElement;
+    render?: React.ReactElement<React.ComponentPropsWithRef<'button'>>;
   }
 }
diff --git a/docs/src/blocks/GoogleAnalytics.tsx b/docs/src/blocks/GoogleAnalytics.tsx
index 5883fec613..a1e83a8c5a 100644
--- a/docs/src/blocks/GoogleAnalytics.tsx
+++ b/docs/src/blocks/GoogleAnalytics.tsx
@@ -26,12 +26,12 @@ const GoogleAnalytics = React.memo(function GoogleAnalytics(props: GoogleAnalyti
     }
   }, []);
 
-  const timeout = React.useRef<NodeJS.Timeout>();
+  const timeout = React.useRef<ReturnType<typeof setTimeout> | null>(null);
 
   React.useEffect(() => {
     // Wait for the title to be updated.
     // React fires useEffect twice in dev mode
-    clearTimeout(timeout.current);
+    clearTimeout(timeout.current ?? undefined);
     timeout.current = setTimeout(() => {
       // Remove hash as it's never sent to the server
       // https://github.com/vercel/next.js/issues/25202
diff --git a/docs/src/design-system/ToggleButtonGroup.tsx b/docs/src/design-system/ToggleButtonGroup.tsx
index cf3a1eab00..00ced02b1d 100644
--- a/docs/src/design-system/ToggleButtonGroup.tsx
+++ b/docs/src/design-system/ToggleButtonGroup.tsx
@@ -47,4 +47,4 @@ export const ToggleButtonGroup = React.forwardRef(function ToggleButtonGroup<
   );
 }) as <Option extends { value: string; label: string }>(
   props: ToggleButtonGroupProps<Option> & { ref?: React.Ref<HTMLDivElement> },
-) => JSX.Element;
+) => React.JSX.Element;
diff --git a/docs/src/design-system/Tooltip.tsx b/docs/src/design-system/Tooltip.tsx
index 1d0e04219e..c18a043e4f 100644
--- a/docs/src/design-system/Tooltip.tsx
+++ b/docs/src/design-system/Tooltip.tsx
@@ -26,7 +26,7 @@ export function Tooltip(props: Tooltip.Props) {
 export namespace Tooltip {
   export interface Props {
     label: string;
-    children: React.ReactElement;
+    children: React.ReactElement<unknown>;
     side?: 'top' | 'right' | 'bottom' | 'left';
   }
 }
diff --git a/packages/mui-base/src/AlertDialog/Backdrop/AlertDialogBackdrop.test.tsx b/packages/mui-base/src/AlertDialog/Backdrop/AlertDialogBackdrop.test.tsx
index 8d84df3ed6..323a65516c 100644
--- a/packages/mui-base/src/AlertDialog/Backdrop/AlertDialogBackdrop.test.tsx
+++ b/packages/mui-base/src/AlertDialog/Backdrop/AlertDialogBackdrop.test.tsx
@@ -10,7 +10,7 @@ describe('<AlertDialog.Backdrop />', () => {
     refInstanceof: window.HTMLDivElement,
     render: (node) => {
       return render(
-        <AlertDialog.Root open modal={false} animated={false}>
+        <AlertDialog.Root open animated={false}>
           {node}
         </AlertDialog.Root>,
       );
diff --git a/packages/mui-base/src/Checkbox/Root/useCheckboxRoot.ts b/packages/mui-base/src/Checkbox/Root/useCheckboxRoot.ts
index b5d3f313c9..1e129f5bb3 100644
--- a/packages/mui-base/src/Checkbox/Root/useCheckboxRoot.ts
+++ b/packages/mui-base/src/Checkbox/Root/useCheckboxRoot.ts
@@ -10,6 +10,7 @@ import { useEnhancedEffect } from '../../utils/useEnhancedEffect';
 import { useFieldRootContext } from '../../Field/Root/FieldRootContext';
 import { useFieldControlValidation } from '../../Field/Control/useFieldControlValidation';
 import { useField } from '../../Field/useField';
+import { getInertValue } from '../../utils/getInertValue';
 
 export function useCheckboxRoot(params: UseCheckboxRoot.Parameters): UseCheckboxRoot.ReturnValue {
   const {
@@ -126,7 +127,7 @@ export function useCheckboxRoot(params: UseCheckboxRoot.Parameters): UseCheckbox
         type: 'checkbox',
         'aria-hidden': true,
         // @ts-ignore
-        inert: 'true',
+        inert: getInertValue(true),
         onChange(event) {
           // Workaround for https://github.com/facebook/react/issues/9023
           if (event.nativeEvent.defaultPrevented) {
diff --git a/packages/mui-base/src/Collapsible/Content/useCollapsibleContent.ts b/packages/mui-base/src/Collapsible/Content/useCollapsibleContent.ts
index 1af0eb3aa0..b7b23f67a2 100644
--- a/packages/mui-base/src/Collapsible/Content/useCollapsibleContent.ts
+++ b/packages/mui-base/src/Collapsible/Content/useCollapsibleContent.ts
@@ -53,8 +53,8 @@ export function useCollapsibleContent(
 
   const [height, setHeight] = React.useState(0);
 
-  const latestAnimationNameRef = React.useRef<string | undefined>('none');
-  const originalTransitionDurationStyleRef = React.useRef<string | undefined>();
+  const latestAnimationNameRef = React.useRef<string>('none');
+  const originalTransitionDurationStyleRef = React.useRef<string | null>(null);
 
   const isTransitioningRef = React.useRef(false);
 
diff --git a/packages/mui-base/src/Dialog/Popup/useDialogPopup.tsx b/packages/mui-base/src/Dialog/Popup/useDialogPopup.tsx
index 401fa5ef20..42a8ede3a0 100644
--- a/packages/mui-base/src/Dialog/Popup/useDialogPopup.tsx
+++ b/packages/mui-base/src/Dialog/Popup/useDialogPopup.tsx
@@ -29,7 +29,7 @@ export function useDialogPopup(parameters: useDialogPopup.Parameters): useDialog
     onOpenChange,
   });
 
-  const popupRef = React.useRef<HTMLElement | null>(null);
+  const popupRef = React.useRef<HTMLElement>(null);
 
   const dismiss = useDismiss(context, {
     outsidePressEvent: 'mousedown',
diff --git a/packages/mui-base/src/Field/Validity/FieldValidity.test.tsx b/packages/mui-base/src/Field/Validity/FieldValidity.test.tsx
index 62c61d1fec..8974a440bb 100644
--- a/packages/mui-base/src/Field/Validity/FieldValidity.test.tsx
+++ b/packages/mui-base/src/Field/Validity/FieldValidity.test.tsx
@@ -23,7 +23,7 @@ describe('<Field.Validity />', () => {
     fireEvent.change(input, { target: { value: 'test' } });
     fireEvent.blur(input);
 
-    const [data] = handleValidity.args[8];
+    const [data] = handleValidity.lastCall.args;
 
     expect(data.value).to.equal('test');
     expect(data.validity.valueMissing).to.equal(false);
@@ -44,8 +44,8 @@ describe('<Field.Validity />', () => {
     fireEvent.focus(input);
     fireEvent.blur(input);
 
-    expect(handleValidity.args[6][0].error).to.equal('error');
-    expect(handleValidity.args[6][0].errors).to.deep.equal(['error']);
+    expect(handleValidity.lastCall.args[0].error).to.equal('error');
+    expect(handleValidity.lastCall.args[0].errors).to.deep.equal(['error']);
   });
 
   it('should correctly pass errors when validate function returns an array of strings', () => {
@@ -63,7 +63,7 @@ describe('<Field.Validity />', () => {
     fireEvent.focus(input);
     fireEvent.blur(input);
 
-    expect(handleValidity.args[6][0].error).to.equal('1');
-    expect(handleValidity.args[6][0].errors).to.deep.equal(['1', '2']);
+    expect(handleValidity.lastCall.args[0].error).to.equal('1');
+    expect(handleValidity.lastCall.args[0].errors).to.deep.equal(['1', '2']);
   });
 });
diff --git a/packages/mui-base/src/Menu/Positioner/useMenuPositioner.ts b/packages/mui-base/src/Menu/Positioner/useMenuPositioner.ts
index 02c1890eb5..46ea58744b 100644
--- a/packages/mui-base/src/Menu/Positioner/useMenuPositioner.ts
+++ b/packages/mui-base/src/Menu/Positioner/useMenuPositioner.ts
@@ -11,6 +11,7 @@ import type {
 import { mergeReactProps } from '../../utils/mergeReactProps';
 import { useAnchorPositioning } from '../../utils/useAnchorPositioning';
 import type { GenericHTMLProps } from '../../utils/types';
+import { getInertValue } from '../../utils/getInertValue';
 
 export function useMenuPositioner(
   params: useMenuPositioner.Parameters,
@@ -43,7 +44,7 @@ export function useMenuPositioner(
           zIndex: 2147483647, // max z-index
         },
         'aria-hidden': !open || undefined,
-        inert: !open ? '' : undefined,
+        inert: getInertValue(!open),
       });
     },
     [positionerStyles, open, keepMounted, hidden],
diff --git a/packages/mui-base/src/NoSsr/NoSsr.tsx b/packages/mui-base/src/NoSsr/NoSsr.tsx
index 9a472f834f..18bf1dda18 100644
--- a/packages/mui-base/src/NoSsr/NoSsr.tsx
+++ b/packages/mui-base/src/NoSsr/NoSsr.tsx
@@ -22,7 +22,7 @@ import { NoSsrProps } from './NoSsr.types';
  *
  * - [NoSsr API](https://base-ui.netlify.app/components/react-no-ssr/#api-reference-NoSsr)
  */
-function NoSsr(props: NoSsrProps): JSX.Element {
+function NoSsr(props: NoSsrProps): React.JSX.Element {
   const { children, defer = false, fallback = null } = props;
   const [mountedState, setMountedState] = React.useState(false);
 
diff --git a/packages/mui-base/src/NumberField/Root/useNumberFieldRoot.ts b/packages/mui-base/src/NumberField/Root/useNumberFieldRoot.ts
index 5f5ed3f33d..47439071ba 100644
--- a/packages/mui-base/src/NumberField/Root/useNumberFieldRoot.ts
+++ b/packages/mui-base/src/NumberField/Root/useNumberFieldRoot.ts
@@ -883,7 +883,7 @@ export namespace UseNumberFieldRoot {
     isScrubbing: boolean;
     inputRef: ((instance: HTMLInputElement | null) => void) | null;
     scrubHandleRef: React.RefObject<ScrubHandle | null>;
-    scrubAreaRef: React.RefObject<HTMLSpanElement>;
-    scrubAreaCursorRef: React.RefObject<HTMLSpanElement>;
+    scrubAreaRef: React.RefObject<HTMLSpanElement | null>;
+    scrubAreaCursorRef: React.RefObject<HTMLSpanElement | null>;
   }
 }
diff --git a/packages/mui-base/src/NumberField/Root/useScrub.types.ts b/packages/mui-base/src/NumberField/Root/useScrub.types.ts
index 3f97383a35..f38292cb9c 100644
--- a/packages/mui-base/src/NumberField/Root/useScrub.types.ts
+++ b/packages/mui-base/src/NumberField/Root/useScrub.types.ts
@@ -2,7 +2,7 @@ export interface ScrubParams {
   disabled: boolean;
   readOnly: boolean;
   value: number | null;
-  inputRef: React.RefObject<HTMLInputElement>;
+  inputRef: React.RefObject<HTMLInputElement | null>;
   incrementValue: (amount: number, dir: 1 | -1, currentValue?: number | null) => void;
   getStepAmount: () => number | undefined;
 }
diff --git a/packages/mui-base/src/Popover/Positioner/usePopoverPositioner.tsx b/packages/mui-base/src/Popover/Positioner/usePopoverPositioner.tsx
index 4a9c04746e..96380cb96b 100644
--- a/packages/mui-base/src/Popover/Positioner/usePopoverPositioner.tsx
+++ b/packages/mui-base/src/Popover/Positioner/usePopoverPositioner.tsx
@@ -9,6 +9,7 @@ import type {
 import { mergeReactProps } from '../../utils/mergeReactProps';
 import { useAnchorPositioning } from '../../utils/useAnchorPositioning';
 import type { GenericHTMLProps } from '../../utils/types';
+import { getInertValue } from '../../utils/getInertValue';
 
 export function usePopoverPositioner(
   params: usePopoverPositioner.Parameters,
@@ -38,7 +39,7 @@ export function usePopoverPositioner(
         return mergeReactProps<'div'>(externalProps, {
           role: 'presentation',
           // @ts-ignore
-          inert: open ? undefined : 'true',
+          inert: getInertValue(open),
           style: {
             ...positionerStyles,
             ...hiddenStyles,
diff --git a/packages/mui-base/src/Popover/Root/PopoverRootContext.ts b/packages/mui-base/src/Popover/Root/PopoverRootContext.ts
index da3e905f29..3e696ad04b 100644
--- a/packages/mui-base/src/Popover/Root/PopoverRootContext.ts
+++ b/packages/mui-base/src/Popover/Root/PopoverRootContext.ts
@@ -12,7 +12,7 @@ export interface PopoverRootContext {
   setTriggerElement: (el: Element | null) => void;
   positionerElement: HTMLElement | null;
   setPositionerElement: (el: HTMLElement | null) => void;
-  popupRef: React.RefObject<HTMLElement>;
+  popupRef: React.RefObject<HTMLElement | null>;
   delay: number;
   closeDelay: number;
   delayType: 'rest' | 'hover';
diff --git a/packages/mui-base/src/Popover/Root/usePopoverRoot.ts b/packages/mui-base/src/Popover/Root/usePopoverRoot.ts
index 6a3144a36b..a1b2011773 100644
--- a/packages/mui-base/src/Popover/Root/usePopoverRoot.ts
+++ b/packages/mui-base/src/Popover/Root/usePopoverRoot.ts
@@ -230,6 +230,6 @@ export namespace usePopoverRoot {
     setTriggerElement: React.Dispatch<React.SetStateAction<Element | null>>;
     positionerElement: HTMLElement | null;
     setPositionerElement: React.Dispatch<React.SetStateAction<HTMLElement | null>>;
-    popupRef: React.RefObject<HTMLElement>;
+    popupRef: React.RefObject<HTMLElement | null>;
   }
 }
diff --git a/packages/mui-base/src/PreviewCard/Root/PreviewCardContext.ts b/packages/mui-base/src/PreviewCard/Root/PreviewCardContext.ts
index af79685930..f3e6b1291c 100644
--- a/packages/mui-base/src/PreviewCard/Root/PreviewCardContext.ts
+++ b/packages/mui-base/src/PreviewCard/Root/PreviewCardContext.ts
@@ -20,7 +20,7 @@ export interface PreviewCardRootContext {
   getRootPopupProps: (externalProps?: GenericHTMLProps) => GenericHTMLProps;
   floatingRootContext: FloatingRootContext;
   transitionStatus: TransitionStatus;
-  popupRef: React.RefObject<HTMLElement>;
+  popupRef: React.RefObject<HTMLElement | null>;
 }
 
 export const PreviewCardRootContext = React.createContext<PreviewCardRootContext | null>(null);
diff --git a/packages/mui-base/src/PreviewCard/Root/usePreviewCardRoot.ts b/packages/mui-base/src/PreviewCard/Root/usePreviewCardRoot.ts
index 1d92e5b4a7..1e9e3dc642 100644
--- a/packages/mui-base/src/PreviewCard/Root/usePreviewCardRoot.ts
+++ b/packages/mui-base/src/PreviewCard/Root/usePreviewCardRoot.ts
@@ -221,6 +221,6 @@ export namespace usePreviewCardRoot {
     setTriggerElement: React.Dispatch<React.SetStateAction<Element | null>>;
     positionerElement: HTMLElement | null;
     setPositionerElement: React.Dispatch<React.SetStateAction<HTMLElement | null>>;
-    popupRef: React.RefObject<HTMLDivElement>;
+    popupRef: React.RefObject<HTMLDivElement | null>;
   }
 }
diff --git a/packages/mui-base/src/Slider/Control/useSliderControl.ts b/packages/mui-base/src/Slider/Control/useSliderControl.ts
index 6e20b6cdaa..039dba32af 100644
--- a/packages/mui-base/src/Slider/Control/useSliderControl.ts
+++ b/packages/mui-base/src/Slider/Control/useSliderControl.ts
@@ -38,7 +38,7 @@ export function useSliderControl(
   const handleRootRef = useForkRef(externalRef, registerSliderControl, controlRef);
 
   // A number that uniquely identifies the current finger in the touch session.
-  const touchIdRef = React.useRef<number>();
+  const touchIdRef = React.useRef<number | null>(null);
 
   const moveCountRef = React.useRef(0);
 
@@ -123,7 +123,7 @@ export function useSliderControl(
       onValueCommitted(newFingerValue.newValue, nativeEvent);
     }
 
-    touchIdRef.current = undefined;
+    touchIdRef.current = null;
 
     // eslint-disable-next-line @typescript-eslint/no-use-before-define
     stopListening();
diff --git a/packages/mui-base/src/Slider/Root/SliderRoot.types.ts b/packages/mui-base/src/Slider/Root/SliderRoot.types.ts
index de137e0b37..4eefca63ee 100644
--- a/packages/mui-base/src/Slider/Root/SliderRoot.types.ts
+++ b/packages/mui-base/src/Slider/Root/SliderRoot.types.ts
@@ -4,8 +4,8 @@ import type { FieldRootOwnerState } from '../../Field/Root/FieldRoot.types';
 
 export interface SliderThumbMetadata {
   inputId: string;
-  ref: React.RefObject<HTMLElement>;
-  inputRef: React.RefObject<HTMLInputElement>;
+  ref: React.RefObject<HTMLElement | null>;
+  inputRef: React.RefObject<HTMLInputElement | null>;
 }
 
 export type SliderContextValue = Omit<
diff --git a/packages/mui-base/src/Slider/Root/useSliderRoot.ts b/packages/mui-base/src/Slider/Root/useSliderRoot.ts
index 2360c0818a..ecce38de00 100644
--- a/packages/mui-base/src/Slider/Root/useSliderRoot.ts
+++ b/packages/mui-base/src/Slider/Root/useSliderRoot.ts
@@ -295,7 +295,7 @@ function useSliderRoot(parameters: UseSliderParameters): UseSliderReturnValue {
 
   const isRtl = direction === 'rtl';
 
-  const previousIndexRef = React.useRef<number>();
+  const previousIndexRef = React.useRef<number | null>(null);
   let axis = orientation;
   if (isRtl && orientation === 'horizontal') {
     axis += '-reverse';
diff --git a/packages/mui-base/src/Slider/Thumb/SliderThumb.tsx b/packages/mui-base/src/Slider/Thumb/SliderThumb.tsx
index 867db5bdd8..8a712fceb3 100644
--- a/packages/mui-base/src/Slider/Thumb/SliderThumb.tsx
+++ b/packages/mui-base/src/Slider/Thumb/SliderThumb.tsx
@@ -8,6 +8,7 @@ import { useForkRef } from '../../utils/useForkRef';
 import { useSliderContext } from '../Root/SliderProvider';
 import { SliderThumbProps } from './SliderThumb.types';
 import { useSliderThumb } from './useSliderThumb';
+import { isReactVersionAtLeast } from '../../utils/reactVersion';
 
 function defaultRender(
   props: React.ComponentPropsWithRef<'span'>,
@@ -70,7 +71,12 @@ const SliderThumb = React.forwardRef(function SliderThumb(
     values,
   } = useSliderContext();
 
-  const mergedRef = useForkRef(typeof render === 'function' ? null : render.ref, forwardedRef);
+  let renderPropRef = null;
+  if (typeof render !== 'function') {
+    renderPropRef = isReactVersionAtLeast(19) ? (render.props as any).ref : render.ref;
+  }
+
+  const mergedRef = useForkRef(renderPropRef, forwardedRef);
 
   const { getRootProps, getThumbInputProps, disabled, index } = useSliderThumb({
     active: activeIndex,
@@ -114,13 +120,13 @@ const SliderThumb = React.forwardRef(function SliderThumb(
     return render(thumbProps, inputProps, ownerState);
   }
 
-  const { children: renderPropsChildren, ...otherRenderProps } = render.props;
+  const { children: renderPropsChildren, ...otherRenderProps } =
+    render.props as React.PropsWithChildren<unknown>;
 
   const children = thumbProps.children ?? renderPropsChildren;
 
-  return React.cloneElement(
-    render,
-    mergeReactProps(otherRenderProps, {
+  return React.cloneElement(render, {
+    ...mergeReactProps(otherRenderProps, {
       ...thumbProps,
       children: (
         <React.Fragment>
@@ -129,7 +135,9 @@ const SliderThumb = React.forwardRef(function SliderThumb(
         </React.Fragment>
       ),
     }),
-  );
+    // @ts-ignore
+    ref: thumbProps.ref,
+  });
 });
 
 SliderThumb.propTypes /* remove-proptypes */ = {
diff --git a/packages/mui-base/src/Slider/Thumb/SliderThumb.types.ts b/packages/mui-base/src/Slider/Thumb/SliderThumb.types.ts
index 84fe617637..4511630217 100644
--- a/packages/mui-base/src/Slider/Thumb/SliderThumb.types.ts
+++ b/packages/mui-base/src/Slider/Thumb/SliderThumb.types.ts
@@ -19,8 +19,8 @@ export interface SliderThumbProps
         props: React.ComponentPropsWithRef<'span'>,
         inputProps: React.ComponentPropsWithRef<'input'>,
         state: SliderThumbOwnerState,
-      ) => React.ReactElement)
-    | (React.ReactElement & { ref: React.Ref<Element> });
+      ) => React.ReactElement<Record<string, unknown>>)
+    | (React.ReactElement<Record<string, unknown>> & { ref: React.Ref<Element> });
 }
 
 export interface UseSliderThumbParameters
diff --git a/packages/mui-base/src/Tabs/Root/useTabsRoot.ts b/packages/mui-base/src/Tabs/Root/useTabsRoot.ts
index eef11ee315..36d867a4a1 100644
--- a/packages/mui-base/src/Tabs/Root/useTabsRoot.ts
+++ b/packages/mui-base/src/Tabs/Root/useTabsRoot.ts
@@ -13,7 +13,7 @@ import { useControlled } from '../../utils/useControlled';
 export interface TabMetadata {
   disabled: boolean;
   id: string | undefined;
-  ref: React.RefObject<HTMLElement>;
+  ref: React.RefObject<HTMLElement | null>;
 }
 
 type IdLookupFunction = (id: any) => string | undefined;
diff --git a/packages/mui-base/src/Tabs/TabsList/TabsListContext.ts b/packages/mui-base/src/Tabs/TabsList/TabsListContext.ts
index cf2b2bcbfe..c8d8a6ddf1 100644
--- a/packages/mui-base/src/Tabs/TabsList/TabsListContext.ts
+++ b/packages/mui-base/src/Tabs/TabsList/TabsListContext.ts
@@ -4,7 +4,7 @@ import * as React from 'react';
 export type TabsListContextValue = {
   activateOnFocus: boolean;
   getTabElement: (value: any) => HTMLElement | null;
-  tabsListRef: React.RefObject<HTMLElement>;
+  tabsListRef: React.RefObject<HTMLElement | null>;
 };
 
 export const TabsListContext = React.createContext<TabsListContextValue | undefined>(undefined);
diff --git a/packages/mui-base/src/Tabs/TabsList/useTabsList.ts b/packages/mui-base/src/Tabs/TabsList/useTabsList.ts
index cabec225fc..07fe4272f6 100644
--- a/packages/mui-base/src/Tabs/TabsList/useTabsList.ts
+++ b/packages/mui-base/src/Tabs/TabsList/useTabsList.ts
@@ -62,7 +62,7 @@ function useTabsList(parameters: UseTabsListParameters): UseTabsListReturnValue
     listOrientation = direction === 'rtl' ? 'horizontal-rtl' : 'horizontal-ltr';
   }
 
-  const tabsListRef = React.useRef<HTMLElement | null>(null);
+  const tabsListRef = React.useRef<HTMLElement>(null);
   const detectActivationDirection = useActivationDirectionDetector(
     value,
     orientation,
@@ -194,7 +194,7 @@ function getInset(tab: HTMLElement, tabsList: HTMLElement) {
 function useActivationDirectionDetector(
   value: any,
   orientation: TabsOrientation,
-  tabsListRef: React.RefObject<HTMLElement>,
+  tabsListRef: React.RefObject<HTMLElement | null>,
   getTabElement: (tabValue: any) => HTMLElement | null,
 ): (newValue: any) => TabActivationDirection {
   const previousTabEdge = React.useRef<number | null>(null);
diff --git a/packages/mui-base/src/Tooltip/Root/TooltipRootContext.ts b/packages/mui-base/src/Tooltip/Root/TooltipRootContext.ts
index b614789173..b8e57e7f21 100644
--- a/packages/mui-base/src/Tooltip/Root/TooltipRootContext.ts
+++ b/packages/mui-base/src/Tooltip/Root/TooltipRootContext.ts
@@ -11,7 +11,7 @@ export interface TooltipRootContext {
   setTriggerElement: (el: Element | null) => void;
   positionerElement: HTMLElement | null;
   setPositionerElement: (el: HTMLElement | null) => void;
-  popupRef: React.RefObject<HTMLElement>;
+  popupRef: React.RefObject<HTMLElement | null>;
   delay: number;
   closeDelay: number;
   delayType: 'rest' | 'hover';
diff --git a/packages/mui-base/src/Tooltip/Root/useTooltipRoot.ts b/packages/mui-base/src/Tooltip/Root/useTooltipRoot.ts
index 916a092f07..3933352e59 100644
--- a/packages/mui-base/src/Tooltip/Root/useTooltipRoot.ts
+++ b/packages/mui-base/src/Tooltip/Root/useTooltipRoot.ts
@@ -256,6 +256,6 @@ export namespace useTooltipRoot {
     positionerElement: HTMLElement | null;
     setTriggerElement: React.Dispatch<React.SetStateAction<Element | null>>;
     setPositionerElement: React.Dispatch<React.SetStateAction<HTMLElement | null>>;
-    popupRef: React.RefObject<HTMLElement>;
+    popupRef: React.RefObject<HTMLElement | null>;
   }
 }
diff --git a/packages/mui-base/src/useCompound/useCompound.test.tsx b/packages/mui-base/src/useCompound/useCompound.test.tsx
index c1790ce784..d508805cbf 100644
--- a/packages/mui-base/src/useCompound/useCompound.test.tsx
+++ b/packages/mui-base/src/useCompound/useCompound.test.tsx
@@ -256,7 +256,7 @@ describe('compound components', () => {
 
       function Child() {
         const ref = React.useRef<HTMLLIElement>(null);
-        const { id } = useCompoundItem<string, { ref: React.RefObject<HTMLLIElement> }>(
+        const { id } = useCompoundItem<string, { ref: React.RefObject<HTMLLIElement | null> }>(
           idGenerator,
           React.useMemo(() => ({ ref }), []),
         );
diff --git a/packages/mui-base/src/useCompound/useCompoundParent.ts b/packages/mui-base/src/useCompound/useCompoundParent.ts
index 8cc2dad24b..99f0b20827 100644
--- a/packages/mui-base/src/useCompound/useCompoundParent.ts
+++ b/packages/mui-base/src/useCompound/useCompoundParent.ts
@@ -47,7 +47,10 @@ if (process.env.NODE_ENV !== 'production') {
   CompoundComponentContext.displayName = 'CompoundComponentContext';
 }
 
-export interface UseCompoundParentReturnValue<Key, Subitem extends { ref: React.RefObject<Node> }> {
+export interface UseCompoundParentReturnValue<
+  Key,
+  Subitem extends { ref: React.RefObject<Node | null> },
+> {
   /**
    * The value for the CompoundComponentContext provider.
    */
@@ -63,7 +66,7 @@ export interface UseCompoundParentReturnValue<Key, Subitem extends { ref: React.
 /**
  * Sorts the subitems by their position in the DOM.
  */
-function sortSubitems<Key, Subitem extends { ref: React.RefObject<Node> }>(
+function sortSubitems<Key, Subitem extends { ref: React.RefObject<Node | null> }>(
   subitems: Map<Key, Subitem>,
 ) {
   const subitemsArray = Array.from(subitems.keys()).map((key) => {
@@ -100,7 +103,7 @@ function sortSubitems<Key, Subitem extends { ref: React.RefObject<Node> }>(
  */
 export function useCompoundParent<
   Key,
-  Subitem extends { ref: React.RefObject<Node> },
+  Subitem extends { ref: React.RefObject<Node | null> },
 >(): UseCompoundParentReturnValue<Key, Subitem> {
   const [subitems, setSubitems] = React.useState(new Map<Key, Subitem>());
   const subitemKeys = React.useRef(new Set<Key>());
diff --git a/packages/mui-base/src/utils/evaluateRenderProp.ts b/packages/mui-base/src/utils/evaluateRenderProp.ts
index 4d16d803ec..a87db824e0 100644
--- a/packages/mui-base/src/utils/evaluateRenderProp.ts
+++ b/packages/mui-base/src/utils/evaluateRenderProp.ts
@@ -6,8 +6,8 @@ export function evaluateRenderProp<ElementType extends React.ElementType, OwnerS
   render: BaseUIComponentProps<ElementType, OwnerState>['render'],
   props: React.HTMLAttributes<any> & React.RefAttributes<any>,
   ownerState: OwnerState,
-): React.ReactElement {
+): React.ReactElement<Record<string, unknown>> {
   return typeof render === 'function'
     ? render(props, ownerState)
-    : React.cloneElement(render, mergeReactProps(render.props, props));
+    : React.cloneElement(render, { ...mergeReactProps(render.props, props), ref: props.ref });
 }
diff --git a/packages/mui-base/src/utils/getInertValue.ts b/packages/mui-base/src/utils/getInertValue.ts
new file mode 100644
index 0000000000..c1f1b9c435
--- /dev/null
+++ b/packages/mui-base/src/utils/getInertValue.ts
@@ -0,0 +1,13 @@
+import { isReactVersionAtLeast } from './reactVersion';
+
+/**
+ * Return the inert attribute taking into consideration the React version.
+ * React 19 changed the inert attribute from a string to a boolean.
+ */
+export function getInertValue(value: boolean): any | undefined {
+  if (!value) {
+    return undefined;
+  }
+
+  return isReactVersionAtLeast(19) ? true : 'true';
+}
diff --git a/packages/mui-base/src/utils/reactVersion.ts b/packages/mui-base/src/utils/reactVersion.ts
new file mode 100644
index 0000000000..ca1d75b703
--- /dev/null
+++ b/packages/mui-base/src/utils/reactVersion.ts
@@ -0,0 +1,9 @@
+import * as React from 'react';
+
+const majorVersion = parseInt(React.version.split('.')[0], 10);
+
+type SupportedVersions = 17 | 18 | 19;
+
+export function isReactVersionAtLeast(reactVersionToCheck: SupportedVersions): boolean {
+  return majorVersion >= reactVersionToCheck;
+}
diff --git a/packages/mui-base/src/utils/types.ts b/packages/mui-base/src/utils/types.ts
index 3c8ecf3e8c..a455514fae 100644
--- a/packages/mui-base/src/utils/types.ts
+++ b/packages/mui-base/src/utils/types.ts
@@ -29,7 +29,10 @@ export type WithBaseUIEvent<T> = {
  * @template Props Props to be spread on the rendered element.
  * @template State Component's internal state.
  */
-export type ComponentRenderFn<Props, State> = (props: Props, state: State) => React.ReactElement;
+export type ComponentRenderFn<Props, State> = (
+  props: Props,
+  state: State,
+) => React.ReactElement<unknown>;
 
 /**
  * Props shared by all Base UI components.
@@ -47,5 +50,7 @@ export type BaseUIComponentProps<
   /**
    * A function to customize rendering of the component.
    */
-  render?: ComponentRenderFn<RenderFunctionProps, OwnerState> | React.ReactElement<ElementType>;
+  render?:
+    | ComponentRenderFn<RenderFunctionProps, OwnerState>
+    | React.ReactElement<Record<string, unknown>>;
 };
diff --git a/packages/mui-base/src/utils/useAnimatedElement.ts b/packages/mui-base/src/utils/useAnimatedElement.ts
index e8609c7d6b..3a947023b9 100644
--- a/packages/mui-base/src/utils/useAnimatedElement.ts
+++ b/packages/mui-base/src/utils/useAnimatedElement.ts
@@ -4,7 +4,7 @@ import { useTransitionStatus } from './useTransitionStatus';
 
 interface UseAnimatedElementParameters {
   open: boolean;
-  ref: React.RefObject<HTMLElement>;
+  ref: React.RefObject<HTMLElement | null>;
   enabled: boolean;
 }
 
diff --git a/packages/mui-base/src/utils/useAnimationsFinished.ts b/packages/mui-base/src/utils/useAnimationsFinished.ts
index df2ade6c03..ce5865f1ad 100644
--- a/packages/mui-base/src/utils/useAnimationsFinished.ts
+++ b/packages/mui-base/src/utils/useAnimationsFinished.ts
@@ -6,7 +6,7 @@ import { useEventCallback } from './useEventCallback';
  * Executes a function once all animations have finished on the provided element.
  * @ignore - internal hook.
  */
-export function useAnimationsFinished(ref: React.RefObject<HTMLElement>) {
+export function useAnimationsFinished(ref: React.RefObject<HTMLElement | null>) {
   const frameRef = React.useRef(-1);
 
   const cancelFrames = useEventCallback(() => {
diff --git a/packages/mui-base/src/utils/useComponentRenderer.ts b/packages/mui-base/src/utils/useComponentRenderer.ts
index 0513aafb5d..00788adbfa 100644
--- a/packages/mui-base/src/utils/useComponentRenderer.ts
+++ b/packages/mui-base/src/utils/useComponentRenderer.ts
@@ -17,7 +17,7 @@ export interface ComponentRendererSettings<OwnerState, RenderedElementType exten
    */
   render:
     | ComponentRenderFn<React.HTMLAttributes<any>, OwnerState>
-    | React.ReactElement
+    | React.ReactElement<Record<string, unknown>>
     | keyof typeof defaultRenderFunctions;
   /**
    * The owner state of the component.
@@ -79,7 +79,7 @@ export function useComponentRenderer<
 
   let resolvedRenderProp:
     | ComponentRenderFn<React.HTMLAttributes<any>, OwnerState>
-    | React.ReactElement;
+    | React.ReactElement<Record<string, unknown>>;
 
   if (typeof renderProp === 'string') {
     resolvedRenderProp = defaultRenderFunctions[renderProp];
diff --git a/packages/mui-base/src/utils/useRenderPropForkRef.ts b/packages/mui-base/src/utils/useRenderPropForkRef.ts
index 94028e9338..828a578d9d 100644
--- a/packages/mui-base/src/utils/useRenderPropForkRef.ts
+++ b/packages/mui-base/src/utils/useRenderPropForkRef.ts
@@ -1,5 +1,7 @@
+import * as React from 'react';
 import type { BaseUIComponentProps } from './types';
 import { useForkRef } from './useForkRef';
+import { isReactVersionAtLeast } from './reactVersion';
 
 /**
  * Merges the rendering element's `ref` in addition to the other `ref`s.
@@ -8,7 +10,13 @@ import { useForkRef } from './useForkRef';
 export function useRenderPropForkRef<ElementType extends React.ElementType, OwnerState>(
   render: BaseUIComponentProps<ElementType, OwnerState>['render'],
   ...refs: Array<React.Ref<any>>
-) {
-  const childRef = typeof render !== 'function' ? render.ref : null;
+): React.RefCallback<any> | null {
+  let childRef;
+  if (typeof render !== 'function') {
+    childRef = isReactVersionAtLeast(19) ? render.props.ref : render.ref;
+  } else {
+    childRef = null;
+  }
+
   return useForkRef(childRef, ...refs);
 }
diff --git a/packages/mui-base/test/conformanceTests/className.tsx b/packages/mui-base/test/conformanceTests/className.tsx
index 34ca69fae2..b05efdb4c3 100644
--- a/packages/mui-base/test/conformanceTests/className.tsx
+++ b/packages/mui-base/test/conformanceTests/className.tsx
@@ -1,10 +1,13 @@
 import * as React from 'react';
 import { expect } from 'chai';
-import { type BaseUiConformanceTestsOptions } from '../describeConformance';
+import type {
+  ConformantComponentProps,
+  BaseUiConformanceTestsOptions,
+} from '../describeConformance';
 import { throwMissingPropError } from './utils';
 
 export function testClassName(
-  element: React.ReactElement,
+  element: React.ReactElement<ConformantComponentProps>,
   getOptions: () => BaseUiConformanceTestsOptions,
 ) {
   describe('prop: className', () => {
diff --git a/packages/mui-base/test/conformanceTests/propForwarding.tsx b/packages/mui-base/test/conformanceTests/propForwarding.tsx
index 2ce0ab852f..79d3936a76 100644
--- a/packages/mui-base/test/conformanceTests/propForwarding.tsx
+++ b/packages/mui-base/test/conformanceTests/propForwarding.tsx
@@ -2,10 +2,13 @@ import * as React from 'react';
 import { expect } from 'chai';
 import { flushMicrotasks, randomStringValue } from '@mui/internal-test-utils';
 import { throwMissingPropError } from './utils';
-import { type BaseUiConformanceTestsOptions } from '../describeConformance';
+import type {
+  ConformantComponentProps,
+  BaseUiConformanceTestsOptions,
+} from '../describeConformance';
 
 export function testPropForwarding(
-  element: React.ReactElement,
+  element: React.ReactElement<ConformantComponentProps>,
   getOptions: () => BaseUiConformanceTestsOptions,
 ) {
   const { render, testRenderPropWith: Element = 'div' } = getOptions();
diff --git a/packages/mui-base/test/conformanceTests/refForwarding.tsx b/packages/mui-base/test/conformanceTests/refForwarding.tsx
index 855e0603b5..9279b1df27 100644
--- a/packages/mui-base/test/conformanceTests/refForwarding.tsx
+++ b/packages/mui-base/test/conformanceTests/refForwarding.tsx
@@ -1,10 +1,13 @@
 import * as React from 'react';
 import { expect } from 'chai';
-import { type BaseUiConformanceTestsOptions } from '../describeConformance';
+import type {
+  ConformantComponentProps,
+  BaseUiConformanceTestsOptions,
+} from '../describeConformance';
 import { throwMissingPropError } from './utils';
 
 async function verifyRef(
-  element: React.ReactElement,
+  element: React.ReactElement<ConformantComponentProps>,
   render: BaseUiConformanceTestsOptions['render'],
   onRef: (instance: unknown, element: HTMLElement | null) => void,
 ) {
@@ -22,7 +25,7 @@ async function verifyRef(
 }
 
 export function testRefForwarding(
-  element: React.ReactElement,
+  element: React.ReactElement<ConformantComponentProps>,
   getOptions: () => BaseUiConformanceTestsOptions,
 ) {
   describe('ref', () => {
diff --git a/packages/mui-base/test/conformanceTests/renderProp.tsx b/packages/mui-base/test/conformanceTests/renderProp.tsx
index 2c1fbe2755..59f4e2190e 100644
--- a/packages/mui-base/test/conformanceTests/renderProp.tsx
+++ b/packages/mui-base/test/conformanceTests/renderProp.tsx
@@ -1,11 +1,14 @@
 import * as React from 'react';
 import { expect } from 'chai';
 import { randomStringValue } from '@mui/internal-test-utils';
-import { type BaseUiConformanceTestsOptions } from '../describeConformance';
+import type {
+  ConformantComponentProps,
+  BaseUiConformanceTestsOptions,
+} from '../describeConformance';
 import { throwMissingPropError } from './utils';
 
 export function testRenderProp(
-  element: React.ReactElement,
+  element: React.ReactElement<ConformantComponentProps>,
   getOptions: () => BaseUiConformanceTestsOptions,
 ) {
   const { render, testRenderPropWith: Element = 'div' } = getOptions();
diff --git a/packages/mui-base/test/createRenderer.ts b/packages/mui-base/test/createRenderer.ts
index b26049c4af..a71f560891 100644
--- a/packages/mui-base/test/createRenderer.ts
+++ b/packages/mui-base/test/createRenderer.ts
@@ -9,14 +9,17 @@ import {
 } from '@mui/internal-test-utils';
 
 type BaseUITestRenderer = Omit<Renderer, 'render'> & {
-  render: (element: React.ReactElement, options?: RenderOptions) => Promise<MuiRenderResult>;
+  render: (
+    element: React.ReactElement<unknown>,
+    options?: RenderOptions,
+  ) => Promise<MuiRenderResult>;
 };
 
 export function createRenderer(globalOptions?: CreateRendererOptions): BaseUITestRenderer {
   const createRendererResult = sharedCreateRenderer(globalOptions);
   const { render: originalRender } = createRendererResult;
 
-  const render = async (element: React.ReactElement, options?: RenderOptions) =>
+  const render = async (element: React.ReactElement<unknown>, options?: RenderOptions) =>
     act(async () => {
       const result = await originalRender(element, options);
       await flushMicrotasks();
diff --git a/packages/mui-base/test/describeConformance.tsx b/packages/mui-base/test/describeConformance.tsx
index 3f593af776..d5daea9ac9 100644
--- a/packages/mui-base/test/describeConformance.tsx
+++ b/packages/mui-base/test/describeConformance.tsx
@@ -10,14 +10,25 @@ import { testRefForwarding } from './conformanceTests/refForwarding';
 import { testRenderProp } from './conformanceTests/renderProp';
 import { testClassName } from './conformanceTests/className';
 
+export type ConformantComponentProps = {
+  render?: React.ReactElement<unknown> | ((props: Record<string, unknown>) => React.ReactNode);
+  ref?: React.Ref<unknown>;
+  'data-testid'?: string;
+  className?: string;
+  style?: React.CSSProperties;
+};
+
 export interface BaseUiConformanceTestsOptions
   extends Omit<Partial<ConformanceOptions>, 'render' | 'mount' | 'skip' | 'classes'> {
   render: (
-    element: React.ReactElement<any, string | React.JSXElementConstructor<any>>,
+    element: React.ReactElement<
+      ConformantComponentProps,
+      string | React.JSXElementConstructor<any>
+    >,
     options?: RenderOptions | undefined,
   ) => Promise<MuiRenderResult> | MuiRenderResult;
   skip?: (keyof typeof fullSuite)[];
-  testRenderPropWith?: keyof JSX.IntrinsicElements;
+  testRenderPropWith?: keyof React.JSX.IntrinsicElements;
 }
 
 const fullSuite = {
@@ -28,7 +39,7 @@ const fullSuite = {
 };
 
 function describeConformanceFn(
-  minimalElement: React.ReactElement,
+  minimalElement: React.ReactElement<ConformantComponentProps>,
   getOptions: () => BaseUiConformanceTestsOptions,
 ) {
   const { after: runAfterHook = () => {}, only = Object.keys(fullSuite), skip = [] } = getOptions();
diff --git a/tsconfig.base.json b/tsconfig.base.json
index 9a3e6cab30..33aea3e45d 100644
--- a/tsconfig.base.json
+++ b/tsconfig.base.json
@@ -13,6 +13,7 @@
     "allowSyntheticDefaultImports": true,
     "noErrorTruncation": false,
     "allowJs": true,
+    "skipLibCheck": true,
     "paths": {
       "@base_ui/react": ["./packages/mui-base/src"],
       "@base_ui/react/*": ["./packages/mui-base/src/*"],