diff --git a/src/main/java/com/rallydev/lookback/LookbackApi.java b/src/main/java/com/rallydev/lookback/LookbackApi.java
index ac0cbe6..217d17a 100644
--- a/src/main/java/com/rallydev/lookback/LookbackApi.java
+++ b/src/main/java/com/rallydev/lookback/LookbackApi.java
@@ -50,6 +50,7 @@ public class LookbackApi {
     protected String proxyUserName;
     protected String proxyPassword;
     protected HttpClient client;
+    protected String apikey;
 
 
     /**
@@ -170,6 +171,14 @@ public LookbackApi setServer(String server) {
         return this;
     }
 
+    /**
+     * Set the API key to be used for authentication. If used, do not set username and password. 
+     * @param key - The api key generated by Rally. 
+     */
+    public void setApiKey(String key) {
+        this.apikey = key;
+    }
+
     /**
      * Set the proxy server you wish to communicate through.
      * @param server - The proxy server you wish to use, must include the protocol (e.g. http://myproxy:8080 )
@@ -248,6 +257,9 @@ private LookbackResult buildLookbackResult(HttpResponse response) throws IOExcep
 
     private HttpUriRequest createRequest(String requestJson) throws IOException {
         HttpPost post = new HttpPost(buildUrl());
+        if (this.apikey != null) {
+            post.setHeader("zsessionid", this.apikey);
+        }
         post.setEntity(new StringEntity(requestJson, "UTF-8"));
         return post;
     }