The transformations in the organization of collective action to combat climate change are marked by the growing presence of infra-state and non-state entities. It is in this context that the carbon market architecture of the Western Climate Initiative has emerged. It is embodied by a linking agreement signed in the fall of 2017 by California, Québec and Ontario. However, is the architecture offered in this agreement able to effectively provide the carbon market with the legal and institutional foundations necessary for its maturation and enable the achievement of its environmental and economic objectives? Written from a Québec perspective, this article aims at detailing the institutional functions of the linking agreement and at teasing out the legal issues raised by their implementation.