diff --git a/README.md b/README.md
index 5cd2aa1..17006cc 100644
--- a/README.md
+++ b/README.md
@@ -38,7 +38,7 @@ source .venv/bin/activate
 pip install -e ".[dev]"
 ```
 
-### Run
+### Run Container
 
 ```bash
 export FLASK_APP=wsgi.py
@@ -86,6 +86,12 @@ Open `http://127.0.0.1:8000`.
 docker compose up --build web
 ```
 
+Compose settings are stored in `env`. Update that file to change values such as:
+
+- `SECRET_KEY`
+- `MAX_UPLOAD_SIZE_MB`
+- `OUTPUT_DIRECTORY`
+
 ### Run the test suite in a container
 
 ```bash
diff --git a/compose.yaml b/compose.yaml
index 9aaa058..b78095e 100644
--- a/compose.yaml
+++ b/compose.yaml
@@ -5,15 +5,12 @@ services:
       target: production
     ports:
       - "8000:8000"
-    environment:
-      SECRET_KEY: change-me
-      MAX_UPLOAD_SIZE_MB: "120"
-      OUTPUT_DIRECTORY: /app/instance/outputs
+    env_file:
+      - env
 
   test:
     build:
       context: .
       target: test
-    environment:
-      MAX_UPLOAD_SIZE_MB: "120"
-      OUTPUT_DIRECTORY: /app/instance/outputs
+    env_file:
+      - env
diff --git a/env b/env
new file mode 100644
index 0000000..ddf01ce
--- /dev/null
+++ b/env
@@ -0,0 +1,3 @@
+SECRET_KEY=change-me
+MAX_UPLOAD_SIZE_MB=120
+OUTPUT_DIRECTORY=/app/instance/outputs