This chapter examines whether, and if so, how and why, governance mainstreaming forms a suitable policy response to situations of superdiversity. The concept of governance refers to problem-solving strategies that are developed and implemented in complex networks of actors, including but certainly not limited to government institutions and government policies. The concept of governance mainstreaming has been developed more broadly in other areas such as gender, disability, and environmental governance. Building from this literature, the chapter defines mainstreaming of migration-related diversity as the effort to embed diversity in a generic approach across policy areas as well as policy levels, to establish a whole-society approach to diversity rather than an approach to specific migrant groups, in complex actor networks. The chapter then analyses patterns in the policy approaches to immigrant integration in the United Kingdom, the Netherlands, and France from the conceptual lens of governance mainstreaming, and considers how and why mainstreaming was developed as a governance strategy, and what role superdiversity played in the rationale for and the choice of strategy towards mainstreaming.