When Google launched their website URL shortner tool, goo.gl in September of 2010, they did not provide an accompanying API for web application support. Competitors, like bit.ly, do provide an API for web application support, which gives them an upper-hand with web developers that wish to incorporate the functionality into their creations.
Now, this has changed. The goo.gl tool allows support for web applications using an API, which was launched part of the Google Code Labs. Both documentation and sample "get started" code is available.
From URL shortening and expanding capabilities to analytics and history, the API is on par with competitors, and may even begin to pull ahead as it ventures into the territory of improved security against malicious content.