Conflict between software developers and testers is inevitable. Prior work on such conflict has focused on conflict management but not on its prevention. We addressed the research question: What are the sources of interpersonal conflict between developers and testers in software development? To attempt to answer this, we collected and analyzed 50 developer–tester conflict scenarios from professional software developers and testers. Our results indicated that the sources of conflict fell into three major areas: process, people, and communication. Conflict sources are presented in a category–subcategory–description format. Implications for theory and practice in the proactive management of conflict sources are discussed.