Intergovernmental agreements (IGAs) represent one of the most formal and commonly used instruments for managing intergovernmental relations within federal systems. Through an analysis of the Belgian and Canadian cases, this thesis was designed to test the following hypothesis: while IGAs apparently play similar functions in different federal regimes, the public law systems of different federations treat these negotiated instruments in a radically distinct fashion. While the first branch of the hypothesis is largely confirmed, the second branch requires more by way of nuance. In both federations, IGAs are indeed used to articulate the exercise of exclusive but interconnected competences, to allocate responsibilities, share resources or channel funds from one order of government to another. They are used to create joint organs and outline processes for information-sharing, consultation and dispute resolution. But IGAs also perform less overt functions. They help redesign federal structures on the margins of constitutional norms. They are used to circumvent the formal distribution of powers and to introduce asymmetrical arrangements. They act as substitutes for constitutional reform or serve to by-pass constitutional amendment procedures. They can have a strong symbolic value as a matter of federal realpolitik. The divergence in the legal character of IGAs was assessed in the face of this convergence of functions. The issue of legal status is tackled from three distinct angles. First, intergovernmental agreements are examined as contractual instruments between federal partners. From this perspective, the differences are more a matter of contrary presumptions than of radically different legal status. Indicia for locating IGAs on either side of the threshold of juridicity, taking these presumptions into consideration, as well as limitations germane to the respective public law systems, are identified. Differences in legal status are more notable when IGAs are considered as normative instruments, that is as mechanisms for affecting the rights and obligations of third parties. In Canada, very few of the dozens of IGAs concluded each year are formally given the force of law through the proper technique of statutory incorporation. In Belgium, by contrast, cooperation agreements are mainly conceived as a novel – if ill defined – type of negotiated norm of public law. Legislative assent is frequently granted, which confers on Belgian IGAs legal force erga omnes in the legal orders of every party to them. Finally, the main difference between the two systems may lie in the place which IGAs occupy in the hierarchy of norms. In Canada, federal partners may legislate in contradiction with an IGA. While the issue remains unresolved in Belgium, doctrinal arguments have been advanced to seek to protect cooperation agreements from unilateral repudiation. These differences concerning the hierarchy of norms reflect a distinct way of resolving the tension that exists between democratic freedom – including the power of assemblies to change their mind – and the stability of intergovernmental relations within a federal regime.