The principles of the best interest of children and subsidiarity constitute the conceptual foundation of the Convention on Protection of Children and Co-Operation in Respect of Intercountry Adoption (HCIA). Subsidiarity in the HCIA dictates a priority for domestic adoption placements for children over intercountry adoption. This article argues against subsidiarity on two fronts. First, the analysis shows that the in-principle priority of domestic adoption cannot be justified on the basis of either heritage rights or state sovereignty. Second, the principle of subsidiarity in the HCIA is a procedural principle, one that stipulates the political/geographical location of the placement of children through a priority ordering. This does not comport with the principle of subsidiarity as it has been conceptualized in ethics and social philosophy, which gives normative structure to the process of decision-making by stipulating the proper level for decisional authority. Subsidiarity in this original sense holds that decisions regarding child welfare should be made at the lowest level possible, by those most affected by the decisions, unless doing so would not be the most suited to protecting and promoting the best interests of children. Appealing to subsidiarity in this theoretical version reveals at least two significant problems with HCIA placement policy and leads to the conclusion that subsidiarity in the HCIA must be formally revised as a structural principle of ethics that will not support the general priority of domestic adoption.