Over fifty million users entrust their professional identities and relationships with LinkedIn, helping build LinkedIn into the largest global professional network today. However, professionals around the world use a wide variety of applications and Web sites to get their work done, and they have spoken loud and clear that they want the ability to leverage their professional networks wherever they work.
Starting today, developers worldwide can integrate LinkedIn into their business applications and Web sites. Developer.linkedin.com is now live and open for business.
The evolution of the LinkedIn Platform
Over the past months, LinkedIn has supported integrations with some of the most prominent and critical software applications in the enterprise. Partnerships with companies like IBM, Blackberry (Research in Motion), and most recently Microsoft, have given us time to invest in both functionality and scalability of the platform.
Source: http://blog.linkedin.com/2009/11/23/linkedin-platform-launch/