The document summarizes lessons learned from building the Yahoo! Developer Network (YDN). It provides a brief history of YDN from 2005 to 2011, outlining its growing focus on developers and open strategies. It describes YDN's technology stack and lessons around SDKs and open source. It discusses both successful and failed partner integration strategies. It also outlines YDN's approaches to developer outreach through forums, Twitter, and Facebook. The final lessons emphasize supporting developers and communities, learning from mistakes, and fostering culture over brand.