Polycentric governance has emergent properties that we argue can be explained through an analysis of the dynamics of institutional change. In this chapter, we use institutional change theories and evolutionary and complex adaptive systems (CAS) thinking to trace mechanisms observed in the change and emergence of polycentric governance. We offer an explanatory model of how polycentric governance changes. Particularly, we consider institutional change of polycentric governance to be negotiated in interdependent (networks of) action situations. Change (or emergence) of governance is the result of endogenous changes (e.g. in power resources actors hold) and/ or of exogenous drivers such as technological change. Polycentric governance shares characteristics with Complex Adaptive Systems (CAS) whose change is evolutionary. We highlight the particular difficulties this perspective entails for assessing institutional performance. We illustrate the evolution of polycentric governance arrangements through two vignettes summarizing case study material from Kenya and Mexico.