Under section 91(27) of Canada’s Constitution Act, 1867 Parliament has jurisdiction over criminal law. The formal characteristics of this concept and its public purposes have developed to take it well beyond its classic concern with prohibiting and punishing immoral conduct. Section 91(27) now supports highly regulatory legislative frameworks addressing not only moral concerns but also areas of well-established provincial regulation such as health and the environment. At the same time, section 92 of the Constitution Act, 1867 allows the provinces considerable jurisdiction to regulate and to create offences in relation to matters that in other aspects fall within section 91(27). The subject of criminal law in the federal context involves unique challenges to the need to retain clear distinctions between federal and provincial powers, while demonstrating the “dominant tide” of federalism which attempts to maximize the operation of federal and provincial statutes without a primary concern for jurisdictional boundaries.