It has been over a decade since organizational researchers began seriously grappling with the phenomenon of multiteam systems (MTSs) as an organizational form spanning traditional team and organizational boundaries. The MTS concept has been met with great enthusiasm as an organizational form that solves both theoretical and practical challenges. However, the development of the MTS domain has been stifled by the absence of theory that clearly delineates the core dimensions influencing the interactions between the individuals and teams operating within them. We contribute to such theory building by creating a multidimensional framework that centers on two key structural features of MTSs—differentiation and dynamism—that create distinct forces affecting individual and team behavior within the system. Differentiation characterizes the degree of difference and separation between MTS component teams at a particular point in time, whereas dynamism describes the variability and instability of the system over time. For each dimension, we discuss the underlying subdimensions that explain how structural features generate boundary-enhancing and disruptive forces in MTSs. We then advance a mesolevel theory of MTS functioning that associates those forces with individuals’ needs and motives, which, in turn, compile upward to form team and MTS emergent states. Finally, we discuss coordination mechanisms that offset or compensate for the structural effects and serve to cohere the MTS component teams. The theoretical and practical implications of our work and an agenda for future research are then discussed.