This thesis explores how selected domestic policies related to energy transition interact with international trade and investment law frameworks. It examines four key categories of policy instruments – subsidies (notably feed-in tariffs and tax credits), local content requirements (LCRs), export restrictions on critical raw materials, and carbon border taxes (with particular focus on the European Union’s Carbon Border Adjustment Mechanism) – assessing their legal limitations under WTO rules and international investment treaties, with reference to other relevant international legal regimes such as international climate law and human rights law. Through a legal-policy analysis, the study highlights tensions between global climate imperatives, the right to development, and energy security, particularly in developing countries. It argues that current international economic law inadequately incorporates sustainable development objectives and is insufficiently aligned with the goals of a just and accelerated global energy transition, resulting in legal uncertainty, fragmentation, and (geo)political frictions. The thesis evaluates key legal and institutional reform proposals – including greater policy space for “green” subsidies and LCRs, and reform or withdrawal from the Energy Charter Treaty – to enable States to implement urgently needed equitable and effective climate and energy policies.