There are nearly 75,000 open source projects and over 750,000 registered users on Sourceforge.net. Yet few of them are successful in attracting other developers and users to participate in the design, testing, and use of the intended software package. Why are some project leaders able to grow their project teams and guide their projects toward completion while others are stalled or abandoned? What attracts participants to a project and why do they continue to work on a project from which they can leave at any time? Using a model based on the Path-Goal Theory of Leadership and self-concept theory, this paper attempts to identify both the sources of motivation for participants in open source projects and the leadership behaviors that attract and motivate them to complete the project.