In most democracies, judicial review of public policies from a constitutional and fundamental rights angle is a key feature of the rule of law. In Belgium, this review exercise is conducted in line with the framework behind the proportionality test, which structures the review by way of three questions: (1) was the government’s action in pursuit of a legitimate aim?; (2) was the action necessary in view of that aim?; and (3) was the action proportionate in view of that aim? The focus of this project is on the first of these questions, which further consists of two subquestions: (1) which aim did the government pursue?; and (2) was this aim legitimate? This project seeks to draft a conceptual framework that provides an answer to these two subquestions, based on a comparative analysis of the practices of the Supreme Court of the United States, the European Court of Human Rights (ECtHR) and the Belgian Council of State, to analyze the Belgian Constitutional Court’s practice on this point, and to subsequently tailor this framework to the analyzed practice of the Constitutional Court. This will generate substantial insight into a historically overlooked part of the proportionality test and will help guide both domestic and international courts’ approaches to purpose review.