diff --git a/README.md b/README.md
index e5dc511..55fd3fa 100644
--- a/README.md
+++ b/README.md
@@ -33,6 +33,19 @@ To start a development server, run:
 * `yarn test:bundle-analyzer` - Generate webpack-bundle-analyzer report
 * `yarn i18n:scrub` - Scrubs i18n locale configs. Adds missing keys and normalizes YAML formatting
 
+## Configuration
+
+Several environment variables are used to configure the application at build-time. None of these values are required during testing.
+
+* `NODE_ENV` - Effects build-time optimizations. Set to `"production"` for builds and unit tests in package.json. Setting to anything else will show a banner in the application's header.
+* `GA_PROPERTY` - Google Analytics property ID.
+* `SENTRY_KEY` - Sentry.io DSN key for error reporting.
+* `CIRCLE_BRANCH`, `CIRCLE_BUILD_NUM`, and `CIRCLE_SHA1` - CircleCI values used to generate build ID. Displayed in application footer and used in Sentry.io error reports.
+* `DEPLOY_BUCKET` - AWS S3 bucket to deploy application to when running `yarn deploy`.
+* `DEPLOY_ENV` - Environment the applicatoin will be deployed to. Used to report environment in Sentry.io error reports. Typically set to either "preview" or "production".
+* `BANNER` - Text to display in header banner. Generally generated from `NODE_ENV`
+* `BUILD_ID` - Application build ID. Generated from `CIRCLE_BRANCH`, `CIRCLE_BUILD_NUM`, and `CIRCLE_SHA1` if not set.
+
 ## License
 
 See [LICENSE.txt](/LICENSE.txt) file for licensing details.