Institutions are central actors in governance. This is a common sense statement and requires elaboration, both in theoretical terms and in terms of comparative politics. This chapter discusses the relevance of five approaches to institutional theory for governance. Each of these approaches helps to illuminate the processes of governing, but each also has serious weaknesses as an approach. Further, although the emphasis in institutional theories is generally on the formal institutions of the public sector, informal structures are also relevant and supplement, or compete with formal institutions.