The Jenkins project has an interesting history. It started from scratch in my spare time, and has grown over time to boast 600+ open-source plug-ins developed by 300+ contributors from all around the world. There are several key ingredients, both technical and social, that enabled this model, and I think those ingredients are useful to other projects. In this talk, I'll discuss how the Jenkins project and the community work, what the ingredients are, why they help you attract more developers into your projects, and why it matters. Basically, my points are that (1) to create a thriving software project, one needs a community of developers, (2) to foster a community of developers, you need extensibility (as a means of not getting in their way and in the way of what they want to do with my software), and (3) you also need to make every step leading up to hacking as easy as possible. I, Kohsuke Kawaguchi, am the creator and the lead developer of Jenkins, which boasts more than 550 plug-ins developed independently by contributors from all over the world. So I'd like to think that I'm qualified to speak on this topic. I have been a speaker at numerous technology conferences.