After a short historical background to Canadian doctoral education, the author addresses the differentiation laws, internal (between undergraduate and graduate studies) and external (strong concentration within a limited number of universities) to institutions, which govern all of North American graduate and doctoral studies. He then details Graduate School functions for twelve leading Canadian universities. They tend overall to assume quite similar central roles, promoting institutional priorities and leadership for graduate studies and exercising quality control functions, enhancing criteria of excellence. A historical drift do show Graduate Schools' tension-driven functions and very existence are constantly at stake. Well implemented on the academic terrain, Canadian Graduate Schools are key institutional faculties for today's graduate studies, confronting the many challenges of the socially distributed knowledge production system underpinning modern societies. (Contains 1 table and 11 footnotes.)