Institutionalist perspectives on water services share an interest in how institutions decisively shape a wide range of outcomes, from service performance and service efficiency to patterns of interactions between key stakeholders, the social legitimacy of water arrangements, and the daily routines followed by water professionals. This chapter begins by highlighting the great diversity but also the common core of institutional approaches. Then, it examines the structuring effects of the proximate institutional environment of water utilities, including contracts and performance indicators. It goes on to look at sector-specific, regulatory institutions at the national level, before further broadening the perspective by presenting how cross-cutting political institutions also shape the operation of water services. Finally, it briefly sketches some avenues for future institutionalist research.