diff --git a/services/clsi/README.md b/services/clsi/README.md
index 270c06ac5d..e074204c36 100644
--- a/services/clsi/README.md
+++ b/services/clsi/README.md
@@ -5,6 +5,30 @@ A web api for compiling LaTeX documents in the cloud
 
 [![Build Status](https://travis-ci.org/sharelatex/clsi-sharelatex.png?branch=master)](https://travis-ci.org/sharelatex/clsi-sharelatex)
 
+The CLSI provide a RESTful interface to traditional LaTeX tools (or, more generally, any command line tool for composing marked-up documents into a display format such as PDF or HTML). The CLSI listens on the following ports by default:
+
+* TCP/3009 - the RESTful interface
+* TCP/3048 - reports load information
+* TCP/3049 - HTTP interface to control the CLSI service
+
+These defaults can be modified in `config/settings.defaults.coffee`.
+
+The provided `Dockerfile` builds a docker image which has the docker command line tools installed. The configuration in `docker-compose-config.yml` mounts the docker socket, in order that the CLSI container can talk to the docker host it is running in. This allows it to spin up `sibling containers` running an image with a TeX distribution installed to perform the actual compiles.
+
+The CLSI can be configured through the following environment variables:
+
+  * `DOCKER_RUNNER` - Set to true to use sibling containers
+  * `SYNCTEX_BIN_HOST_PATH` - Path to SyncTeX binary
+  * `COMPILES_HOST_DIR` - Working directory for LaTeX compiles
+  * `SQLITE_PATH` - Path to SQLite database
+  * `TEXLIVE_IMAGE` - The TEXLIVE docker image to use for sibling containers, e.g. `gcr.io/overleaf-ops/texlive-full:2017.1`
+  * `TEXLIVE_IMAGE_USER` - When using sibling containers, the user to run as in the TEXLIVE image. Defaults to `tex`
+  * `TEX_LIVE_IMAGE_NAME_OVERRIDE` - The name of the registry for the docker image e.g. `gcr.io/overleaf-ops`
+  * `FILESTORE_DOMAIN_OVERRIDE` - The url for the filestore service e.g.`http://$FILESTORE_HOST:3009`
+  * `STATSD_HOST` - The address of the Statsd service (used by the metrics module)
+  * `LISTEN_ADDRESS` - The address for the RESTful service to listen on. Set to `0.0.0.0` to listen on all network interfaces
+  * `SMOKE_TEST` - Whether to run smoke tests
+
 Installation
 ------------