Recent years have witnessed increased political interest to the challenge of organizing policy integration to govern societal problems that crosscut the boundaries of traditional government sectors and levels, including climate change, food insecurity, terrorism, and the instability of financial markets. Public policy scholars have recently suggested to study such attempts by conceptualizing policy integration as a multi-dimensional process. Although such a processual perspective has helped to comparatively assess policy (dis)integration, the mechanisms of (dis)integration over time remain undertheorized. Past studies have reported a number of relevant factors, but these have remained rather functionalistic observations that lack explanatory value. To address this gap, we propose a mechanism-based approach that uncovers the political processes that underlie policy (dis)integration over time. Rooted in different strands of social science literature, the mechanistic approach offers a model of causation to assess the plausible chain of key processes that are triggered under particular contextual conditions. We illustrate the framework by empirically investigating the mechanisms that explain the policy (dis)integration of food and climate change adaptation policy in the Netherlands. We end the paper with discussing various implications of our findings for processual approaches to policy integration.