This research paper critically examines the relationship between law and morality with special reference to H.L.A. Hart’s positivist theory. The study focuses on Hart’s separation thesis, according to which the existence and validity of law are conceptually distinct from the moral merit of law. It explains Hart’s distinction between primary and secondary rules, the rule of recognition, the internal point of view, and his minimum content of natural law. The paper then considers Lon Fuller’s response, particularly the inner morality of law and the eight principles of legality, and applies the Hart-Fuller debate to the German ‘Grudge Informer’ case arising from the Nazi period. The analysis also considers objections raised by Ronald Dworkin and John Finnis, together with Joseph Raz’s exclusive-positivist reply, and examines Hart’s later accommodation of moral criteria through the idea of inclusive positivism. The study further considers the relevance of these theories to contemporary constitutional systems, with particular reference to India and the relationship between constitutional validity, fundamental rights, and constitutional morality. The research adopts a doctrinal and analytical methodology, relying on primary and secondary legal materials, including Hart’s works, Fuller’s writings, leading jurisprudential scholarship, and relevant case law. The paper finds that Hart does not deny the practical relationship between law and morality; rather, he rejects the claim that moral validity is a necessary condition of legal validity. At the same time, Hart’s minimum content and inclusive positivism demonstrate the practical possibility of moral criteria entering legal systems through accepted legal rules. The paper therefore treats the Hart-Fuller debate as a continuing analytical framework for understanding the distinction and interaction between legality, morality, and constitutional values.