Service engineers often struggle to locate the relevant Web services needed to satisfy users' requests. The authors describe how service engineers can capitalize on Web services' interactions - namely, collaboration, substitution, and competition - to build social networks for service discovery. Through these networks, Web services identify those peers with which they'd like to work, those that can replace them in case of failure, and those that compete against them for selection. Building a Web service's social network requires six steps, which the article describes. © 2011 IEEE.