Abstract Empirical scholars have set out to refute legalism in a simple version. Legalism has been said to hold that ‘the law is “out there”, distinct from morals and politics, legal rules are determinate, the legal system is complete’. These elements stem from different and partially contradicting legal theories: the declaratory theory of law, formalism, and positivism. The chapter traces the roots of simple legalism following a comparative approach across disciplines (empirical and doctrinal), within legal scholarship, and between the common law and civil law. It finds that except for a certain form of positivism, legal scholarship has produced theories of the law that do not describe what judges do but define what considerations the legal community accepts as legal and what it criticizes as illegal. Therefore, as others have stressed before, empirical studies of judicial decision-making must take a stand in the normative dispute about what the law is when they argue that judges are guided by extra-legal factors. The chapter identifies three promising strands for future empirical research on legalism: a more appropriate benchmark of measuring extra-legal attitudinal influence, the impact of legal narratives on judicial behaviour, and a focus on lower courts.