diff --git a/README.md b/README.md
index 489e44f..63cdb15 100644
--- a/README.md
+++ b/README.md
@@ -70,6 +70,12 @@ After installation:
 
 That's it! You now have an organized CSS foundation to build on.
 
+## Using Roux with Rails
+
+Rails 8 uses Propshaft by default, which does not support CSS `@import` directives. Even in setups that do support it, the raw `@import` approach tells the browser to load each file as a separate network request, which hurts performance. A CSS bundler compiles all your imports into a single file, solving both problems.
+
+You're free to use any bundler you prefer, but if you want a "just set this up for me" path, follow our [Rails setup guide] using cssbundling-rails and PostCSS.
+
 ## How it works
 
 Everything is imported into `app.css`, which you'll compile into one CSS file (or import directly).
@@ -567,6 +573,7 @@ We are [available for hire][hire].
 <!-- END /templates/footer.md -->
 
 [bitters]: https://github.com/thoughtbot/bitters
+[Rails setup guide]: guides/rails-setup.md
 [codepen]: https://codepen.io/enatario/pen/LEppZLZ
 [custom properties]: https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_cascading_variables/Using_CSS_custom_properties
 [lightning CSS]: https://lightningcss.dev/
diff --git a/guides/rails-setup.md b/guides/rails-setup.md
new file mode 100644
index 0000000..b91cba3
--- /dev/null
+++ b/guides/rails-setup.md
@@ -0,0 +1,63 @@
+# Setting Up Roux with Rails
+
+Rails 8 uses [Propshaft] by default, which does not support CSS `@import` directives. Even in setups that do support it, the raw `@import` approach tells the browser to load each file as a separate network request, which hurts performance. A CSS bundler compiles all your imports into a single file, solving both problems.
+
+The steps below use [cssbundling-rails] with PostCSS. You're free to use any bundler you prefer.
+
+> **Tip:** Starting a new app? `rails new myapp --css postcss` handles most of this for you. Just run Roux's `init` command and move the files into place.
+
+## Using the script
+
+You can use this script two ways:
+
+**Copy and paste** the commands directly into your terminal, skipping any steps you've already completed.
+
+**Or run it as a shell script:**
+
+1. Create a file called `roux-on-rails-setup.sh` and paste the contents in
+2. Make it executable: `chmod +x roux-on-rails-setup.sh`
+3. Run it: `./roux-on-rails-setup.sh`
+4. Delete the file when done
+
+The script checks whether each step has already been done before running, so it's safe to run on a partially configured project.
+
+```bash
+#!/usr/bin/env bash
+set -e
+
+# Copy Roux's CSS files
+npx github:thoughtbot/roux init
+
+# Add cssbundling-rails gem if not already present
+grep -q "cssbundling-rails" Gemfile || bundle add cssbundling-rails
+
+# Install yarn if not already available
+command -v yarn >/dev/null 2>&1 || npm install --global yarn
+
+# Run PostCSS install if not already configured
+[ -f postcss.config.js ] || bin/rails css:install:postcss
+
+# Copy all Roux files into Rails' stylesheet directory, then rename app.css
+# to the PostCSS entry point, overwriting the scaffolded default
+cp -r css/. app/assets/stylesheets/
+mv app/assets/stylesheets/app.css app/assets/stylesheets/application.postcss.css
+
+if [ -f app/assets/stylesheets/application.css ]; then
+  echo ""
+  echo "Found app/assets/stylesheets/application.css."
+  echo "On a brand new Rails app this file is safe to delete."
+  echo "If you have existing styles in it, you should port them to Roux's files manually first."
+  read -r -p "Delete application.css? [y/N] " response
+  if [[ "$response" =~ ^[Yy]$ ]]; then
+    rm app/assets/stylesheets/application.css
+  else
+    echo "Skipping. You'll need to manually remove or update application.css before your styles will compile correctly."
+  fi
+fi
+
+# Clean up
+rm -rf css/
+```
+
+[cssbundling-rails]: https://github.com/rails/cssbundling-rails
+[Propshaft]: https://github.com/rails/propshaft