The International Relations Unit at the Department of Political Science is proud to announce the second contribution to its new series of working papers, the Mainz Papers on International and European Politics (MPIEP): “Theorising Regionalism and External Influence: A Situation-structural Approach” authored by Johannes Muntschick (University of Mainz) continues the MPIEP series. The paper proposes an innovative theoretical approach to the analysis of regionalism by taking the impact of extra-regional relations and the influence of external actors explicitly into account. Its central assumptions are elucidated by brief plausibility probes on empirical examples from the Southern African Development Community (SADC), notably concerning regional economic, infrastructure and security cooperation.