Prominent conceptualizations of policy coherence for sustainable development focus primarily on the roles of intra-governmental policy processes and institutional interactions in shaping coherence between various agendas and policies. These technocratic understandings of coherence overlook the more political drivers of coherence, such as the vested interests or ideologies that may encourage or hinder efforts to achieve coherence. This paper addresses this gap by drawing on the comparative politics literature to facilitate a political understanding of policy coherence. It introduces an analytical framework hypothesizing how ideas, institutions, and interests (the three I's) may influence policy coherence at different policy stages. As such, it includes measures of how policy coherence is applied by different actors and institutions, and whose ideas and interests may be served by pursuing or not pursuing coherence. This article provides an example of how the framework can be applied to study policy coherence between two prominent international agendas: Agenda 2030 (incorporating the Sustainable Development Goals) and the Paris Agreement. Overall, the paper argues that the three I's influence policy options and shape the ambition and importance given to different agendas, goals and actors in pursuing or resisting policy coherence. This framework is suited for assessing the political divers of policy coherence through being applied to empirical data at global or national levels.