Since emerging in the late 1970s and early 1980s, neo-institutional theory has been a popular framework for understanding law, legal institutions, and policies on the books and in action. Neo-institutional theory has been particularly useful for explaining diverse criminal justice phenomena, from changes in penal law and policy statements to on-the-ground practices across police departments, courts, carceral facilities, and community corrections. This review describes how scholars of the criminal legal system have used neo-institutional theory and where there is room for further utilization. Additionally, it discusses how and why neo-institutional theory is particularly useful for sociolegal scholars, and not only those studying criminal legal organizations and policies.