Welcome to the Valve Developer Community. Whether you're building a "Triple-A" commercial project or a MOD for Half-Life® 2, you'll want to sign up as a Valve developer today. Once registered, you'll have unlimited access to the WIKI and discussion areas of this site, inclusion in the developer mailing list, online file hosting space for your project, and more.
Source and the Source SDK
Our knowledgebase of technical information about using the engine and all of the related tools is now posted on a community-driven web site called a WIKI. Sign up as a developer to contribute or to ask a question.
For MOD Teams
Why choose the Source Engine for your MOD?
Source Control (Perforce) Explained
Players Online Reach Record Numbers