State and non-state actors interact in both formal and informal ways during migration governance. Yet, we know little about such interactions, especially in the field of transit migration, a largely regional phenomenon. Here the categories of migrants are fluid between refugees, regular and irregular migrants, including those from conflict regions. Governance takes place also informally. Building on relational theories in International Relations, this article introduces a novel relational approach to polycentric governance. I argue that at the centre of such governance are not simply institutions or migration regimes, but power-laden relations among governmental, non-governmental, supranational, and non-state actors, as well as sending and destination states. These form architectures of partially official, partially informal dynamics that govern transit migration in a particular world region. Such architectures are based on mechanisms of cooperation, conditionality, containment, contestation, and others, combined in regionally specific ways. The mechanisms manifest themselves differently depending on how actors are embedded in places with different political regimes and statehood capacities. The article illustrates this relational perspective to polycentric governance with comparative evidence from the Balkans and the Middle East.