One of the most striking changes in organizations today is the agile boundaries of work teams. Unlike traditional teams with a defined set of employees, today’s work teams exhibit great fluidity: workers now move across the boundaries more freely and frequently. Despite capturing the recent interest of researchers, our understanding of dynamic team membership and its implications remains limited. To fill the void in the existing literature, this study examined an important aspect of membership change (i.e., predictability) that may influence affective emergent states (i.e., team potency and cohesion) and ultimately team effectiveness. This study also examined team role structure as a team contextual factor that shapes the impact of predictable membership change. The results of a laboratory experiment revealed that the predictability of member change is positively associated with team potency after the change. Change predictability is also positively related with team cohesion after the change, but only when the roles in the focal team are undifferentiated. In addition, the results showed that the group emergent states that occur after membership change have unique contributions on team effectiveness over and above the effects of team task-coordination process.