diff --git a/src/lib.rs b/src/lib.rs
index f3b6e807d..60392fb96 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -407,6 +407,12 @@ macro_rules! chain {
 /// return a regular value of some other kind.
 /// [`.next_tuple()`](Itertools::next_tuple) is an example and the first regular
 /// method in the list.
+/// 
+/// # Guarantees
+/// 
+/// Given deterministic inputs, all iterator adapters currently yield items
+/// in a predictable order. This order is considered observable and is therefore
+/// intended to remain stable across releases that share the same major version.
 pub trait Itertools: Iterator {
     // adaptors