When an organization seeks to apply a computerbased application to its business processes, the decision of whether to build or buy software must typically be made. Much previous research has bypassed the build-or-buy decision stage. Even the limited studies focusing on the build-or-buy decision have tended to focus on checklists or guidelines for decision criteria and decision procedures. Thus, the build-or-buy decision process has not been explored fully from the behavioral perspective. The present research provides new insights into decision makers’ actual behavior when making build-or-buy decisions. Based on the belief processing model of Smith, Benson, and Curley (1991), a model is developed to describe the actual cognitive processes involved in the build-or-buy decision. Two hypotheses based on the theoretical background are proposed and will be investigated in an empirical study. We then describe the research methods for the empirical study in some detail. We conclude with a short discussion.