This chapter discusses the structure and management of communities of Web services from two perspectives. The first perspective, called coopetition, shows the simultaneous cooperative and competitive behaviors that Web services exhibit when they reside in the same community. These Web services offer similar functionalities, and hence are competitive, but they can also cooperate as they share the same savoir-faire. The second perspective, called competition, shows the competition that occurs not between Web services but between their communities, which are associated with similar functionalities. To differentiate such communities, a competition model based on a set of metrics is discussed in this chapter.