This essay discusses how multinational cooperation has become a dominant feature of international military operations by examining its dimensions and characteristics, as well as the challenges and chances it poses. The first part of the essay deals with the changes in the international scenarios that have increased the phenomenon. The second part, besides providing some remarks on models and terminology, identifies a number of potential areas of conflict or stress factors between armed forces of cooperating countries. The essay examines not only the challenges to mutual trust and cohesion among all organizational actors but also how from the positive interaction of different national cultures a new hybrid multinational culture may arise. Military sociology, through research on multinational cooperation, could provide new keys of interpretation for the broad intercultural processes and dynamics that characterize today’s societies.