ENThe European Green Deal strategy targets accelerated sustainability transitions, yet the pathways and processes thereto differ markedly across EU member-states, particularly in the energy sector. Politics and institutional contexts largely determine the transition dynamics. However, the sustainability transitions scholarship lacks concrete tools to identify such political barriers to transitions. This paper, therefore, asks: How do political barriers to sustainability transitions emerge and endure, driving differences in transition dynamics across countries? By integrating concepts from institutional economics with the sustainability transitions scholarship (the multi-level perspective), this paper introduces a theoretical framework to assess political barriers to sustainability transitions in their institutional contexts. Additionally, the paper provides empirical evidence from a new region for sustainability transition research: the electricity sectors in the Baltic states of Lithuania, Estonia, and Latvia. The comparative case study relies on 25 semi-structured interviews with senior energy policy stakeholders from the Baltic region, triangulated with content analysis of policy documents. The paper concludes that, first, political barriers to transitions emerge in their institutional contexts as they define the policy objectives (or lack thereof) that reinforce (or reduce) transition processes. Second, political barriers to sustainability transitions endure as lacking incentives, alongside misaligned rules and norms, hinder niche development across countries. This analysis suggests policy changes for policymakers and points to future research avenues. Keywords: energy policy, sustainability transitions, institutions, Latvia, Lithuania, Estonia. [From the publication]