The Vienna Declaration, adopted June 25th, 1993 by the World Conference on Human Rights, enshrines the legal principle of indivisibility of rights and freedoms and its corollary, the absence of legal hierarchy between these rights and freedoms. This International consecration has also found a direct resonance in Canadian law, within which the Supreme Court had clearly integrated this principle in Dagenais v. Canadian Broadcasting Corp., rendered a little less than a year later. Yet for all that it can be coherent on an ideological or philosophical angle, the elimination (or prohibition) of any legal hierarchy between fundamental rights seems very unlikely to be implemented in practice. In the point of view of the authors, the very special nature of the different rights and freedoms enshrined in legal texts on human rights, inextricably linked to a certain moral view of society, underlies the establishment, over time, of a legal hierarchy between fundamental rights and freedoms in the many legal regimes that constitute the international society. Without asserting that the principle of non-hierarchy between fundamental rights must be completely set aside, the authors try to demonstrate that (1) the concept of legal hierarchy between fundamental rights is due to receive a definition not unidimensional, but rather bidimensional (formal and material forms of legal hierarchies); and (2) the main criteria to establish the existence of material hierarchies between fundamental human rights within a given legal system.