Insight into social psychology is relevant for the understanding of how the law works in courtrooms, how people perceive the law as a legal system, and how officials function in several legal contexts, such as in the areas of legal decision making, law making, and law enforcement. In other words, social psychology is needed to understand how the law works (or law in action). Furthermore, in part because both social psychology and law share an emphasis on behavioural regulation, notions about how the law should work (or law in the books) can also profit from an understanding of basic principles of social psychology. Importantly, insights into the social psychology of law are not merely an application of basic social psychological principles in legal contexts. Rather, studying social psychology and the law often provides insights that may well feed into basic social psychological research. Thus, both law and social psychology can learn from each other. In this blog I reflect on the two-way street between law and social psychology.