Boundedness – the distinction between members and non-members – has long been a central defining feature of a team. In this perspective paper, we start by discussing classic conceptualizations of team boundaries, which emphasize the importance of boundary clarity. Yet many teams are more fluid, more overlapping and more dispersed − and consequently their boundaries are less clear − than ever before. We review recent literature that begins to illuminate the changing nature of team boundaries, and argue that fluidity, overlap, and dispersion have important implications for teams through their effects on members’ shared identity and mutual understanding. We propose that today’s teams can be usefully characterized as tightly versus loosely bounded, rather than as clearly bounded by definition, and conclude by examining the implications of the changing nature of team boundaries for future theoretical and empirical research on teams.