diff --git a/README.md b/README.md
index 10f5acbb..42e89bd2 100644
--- a/README.md
+++ b/README.md
@@ -21,23 +21,26 @@ There is also built-in support for using **headless Chrome** to efficiently meas
 
 ### Requirements
 
-`domain-scan` requires **Python 3.5 and up**. To install dependencies:
+`domain-scan` requires **Python 3.5 and up**.
+
+To install **core dependencies**:
 
 ```bash
 pip install -r requirements.txt
 ```
 
-This will automatically allow the use of two scanners:
+You can install scanner- or gatherer-specific dependencies yourself. Or, you can "quick start" by just **installing all dependencies for all scanners and/or all gatherers**:
 
-* `pshtt` - A scanner that uses the [`pshtt`](https://github.com/dhs-ncats/pshtt) Python package from the [Department of Homeland Security's NCATS team](https://github.com/dhs-ncats).
-* `sslyze` - A scanner that uses the [`sslyze`](https://github.com/nabla-c0d3/sslyze) Python package maintained by Alban Diquet.
+```bash
+pip install -r requirements-scanners.txt
+pip install -r requirements-gatherers.txt
+```
 
-Other individual scanners will require additional externally installed dependencies:
-
-* `trustymail`: The `trustymail` command, available from the [`trustymail`](https://github.com/dhs-ncats/trustymail) Python package from the [Department of Homeland Security's NCATS team](https://github.com/dhs-ncats). (Override path by setting the `TRUSTYMAIL_PATH` environment variable.)
-* `a11y`: The `pa11y` command, available from the [`pa11y`](https://www.npmjs.com/package/pa11y) Node package. (Override path by setting the `PA11Y_PATH` environment variable.)
-* `third_parties`: The `phantomas` command, available from the [`phantomas`](https://www.npmjs.com/package/phantomas) Node package. (Override path by setting the `PHANTOMAS_PATH` environment variable.)
+If you plan on **developing/testing domain-scan itself**, install development requirements:
 
+```bash
+pip install -r requirements-dev.txt
+```
 
 ### Usage
 
@@ -65,7 +68,16 @@ Append columns to each row with metadata about the scan itself, such as how long
 ./scan example.com --scan=pshtt --meta
 ```
 
-##### Parallelization
+### Scanners
+
+* `pshtt` - A scanner that uses the [`pshtt`](https://github.com/dhs-ncats/pshtt) Python package from the [Department of Homeland Security's NCATS team](https://github.com/dhs-ncats).
+* `sslyze` - A scanner that uses the [`sslyze`](https://github.com/nabla-c0d3/sslyze) Python package maintained by Alban Diquet.
+* `trustymail`: The `trustymail` command, available from the [`trustymail`](https://github.com/dhs-ncats/trustymail) Python package from the [Department of Homeland Security's NCATS team](https://github.com/dhs-ncats). (Override path by setting the `TRUSTYMAIL_PATH` environment variable.)
+* `third_parties` - What third party web services are in use, using [headless Chrome](https://developers.google.com/web/updates/2017/04/headless-chrome) to trap outgoing requests. (See documentation for [using](#headless-chrome) or [writing](#developing-chrome-scanners) Chrome-based scanners.)
+* `a11y` - Accessibility issues, using [`pa11y`](https://github.com/pa11y/pa11y).
+* `noop` - Test scanner (no-op) used for development and debugging. Does nothing.
+
+### Parallelization
 
 It's important to understand that **scans run in parallel by default**, and **data is streamed to disk immediately** after each scan is done.
 
@@ -117,15 +129,6 @@ See [`docs/lambda.md`](`docs/lambda.md`) for how to build and deploy Lambda-base
 
 ### Options
 
-**Scanners:**
-
-* `pshtt` - HTTP/HTTPS/HSTS configuration, using [`pshtt`](https://github.com/dhs-ncats/pshtt).
-* `trustymail` - MX/SPF/STARTTLS/DMARC configuration, using [`trustymail`](https://github.com/dhs-ncats/trustymail).
-* `sslyze` - TLS/SSL configuration, using [`sslyze`](https://github.com/nabla-c0d3/sslyze).
-* `third_parties` - What third party web services are in use, using [headless Chrome](https://developers.google.com/web/updates/2017/04/headless-chrome) to trap outgoing requests. (See documentation for [using](#headless-chrome) or [writing](#developing-chrome-scanners) Chrome-based scanners.)
-* `a11y` - Accessibility issues, using [`pa11y`](https://github.com/pa11y/pa11y).
-* `noop` - Test scanner (no-op) used for development and debugging. Does nothing.
-
 **General options:**
 
 * `--scan` - **Required.** Comma-separated names of one or more scanners.
diff --git a/lambda/remote_build.sh b/lambda/remote_build.sh
index 4c3e2ef0..c5edde8e 100755
--- a/lambda/remote_build.sh
+++ b/lambda/remote_build.sh
@@ -42,7 +42,7 @@ pip install .
 cd ..
 
 cd domain-scan
-pip install -r requirements.txt
+pip install -r lambda/requirements-lambda.txt
 cd ..
 
 deactivate
diff --git a/lambda/requirements-lambda.txt b/lambda/requirements-lambda.txt
index 18061732..1ca82012 100644
--- a/lambda/requirements-lambda.txt
+++ b/lambda/requirements-lambda.txt
@@ -3,4 +3,3 @@
 
 strict-rfc3339
 publicsuffix
-
diff --git a/requirements-gatherers.txt b/requirements-gatherers.txt
index e374b3c1..91b850da 100644
--- a/requirements-gatherers.txt
+++ b/requirements-gatherers.txt
@@ -1,3 +1,6 @@
+###
+# Requirements used by specific gatherers.
+
 # censys
 google-cloud-bigquery
 google-auth-oauthlib
diff --git a/requirements-scanners.txt b/requirements-scanners.txt
index d519ecac..44ec8416 100644
--- a/requirements-scanners.txt
+++ b/requirements-scanners.txt
@@ -1,7 +1,5 @@
-
-# a11y
-pyyaml
-requests
+###
+# Requirements used by specific scanners.
 
 # pshtt
 git+https://github.com/dhs-ncats/pshtt.git#egg=pshtt
@@ -12,3 +10,7 @@ git+https://github.com/dhs-ncats/trustymail.git#egg=trustymail
 # sslyze
 sslyze>=1.3.4,<1.4.0
 cryptography
+
+# a11y / csp
+pyyaml
+requests
diff --git a/requirements.txt b/requirements.txt
index f462502f..37e38281 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -8,6 +8,6 @@
 # invocation.
 boto3
 
-# Used in Lanbda functions. Also copied to lambda/requirements-lambda.txt.
+# Used in Lambda functions. Also copied to lambda/requirements-lambda.txt.
 strict-rfc3339
 publicsuffix