This book explores some implications of studying international relations from a systemic perspective. This chapter takes on the preliminary tasks of defining systems, identifying distinctive characteristics of systemic explanations, and situating systems approaches in a broader context of relational framings. A system is a bounded set of components of particular types, arranged in definite ways, operating in a specific fashion to produce characteristic outcomes, some of which are emergent. The arrangement and operation of the components produce “emergent” “systems effects;” properties and outcomes that cannot be fully understood through knowledge of the parts considered separately. I emphasize the relational character of systemic explanations and their reliance on mechanisms and processes, in order to foster developing a relational processual systemic perspective within a pluralistic IR.