Researchers in public policy and public administration agree that policy integration is a process. Nevertheless, scholars have given limited attention to political aspects that facilitate or impede integration. This paper aims at filling that gap, by looking at how different theories of the policy process can help in explaining the process of policy integration as shaped by policy subsystems. By building on insights from theories of the policy process, we develop pathways regarding adoption and implementation in policy integration that account for the politicization and the role of actors and subsystems in the policy process. Our main argument is that policy integration is in permanent political tension with the sectoral logic of policymaking, which predominantly happens between actors in subsystems. Policy integration is, thus, not a single moment when those tensions are solved once and for all, but a political process that requires deliberate efforts to overcome the pull toward sector-specific problem definition, policymaking, implementation, and evaluation.