[first paragraph] From the very beginning of this research project, we understood that we needed to define what success meant in open source so that we could use that definition to create a dependent variable for our empirical studies. Does success mean a project has developed high quality software, or does it mean that the software is widely used? How might extremely valuable software that is used by only a few people, such as software for charting parts of the human genome, fit into this definition? In this chapter, we establish a robust success and abandonment measure that satisfies these conditions. We describe the process we went through to create a definition of open source success and abandonment, and how we used that definition to classify nearly all the projects hosted on Sourceforge.net (SF, as of October 2006) as either successful or abandoned.