In modern socio-economic conditions, the issues of sustainable development, sustainable economy, resource efficiency and reduction of greenhouse gas emissions have become relevant, and in this regard, the issues of «green» economy, energy transition are being discussed. However, there are no established legal definitions of the terms "green" economy and «energy transition». In the conditions of energy transition, the issues of the «green economy» are relevant for the states that are members of the Eurasian Economic Union (hereinafter referred to as the EAEU) and the Union State (Russia – Belarus). In the conditions of energy transition, new objects of property rights appear (for example, carbon units), new contractual structures are applied, energy efficiency requirements are established when organizing purchases for state and municipal needs, etc. In this regard, it seems relevant to conduct an analysis of the regulatory legal framework of the «green» energy transition in order to substantiate proposals for the development of legislative support for entrepreneurial (economic) activities in the conditions of energy transition. The purpose of the study is to reveal the legal aspect of the «green» energy transition based on the analysis of regulatory legal acts, program documents, scientific statements about the «green» economy and energy transition. Materials and methods. Regulatory legal acts, program documents in the field of regulation of relations related to energy transition, and special literature have been collected for the analysis. The study was conducted using the methods of generalization and analysis, including comparative one. The results of the study. The legal aspect of ensuring energy efficiency, the formation of a low-carbon economy and the reduction of greenhouse gas emissions, a closed-cycle economy in Russia, in the states of the Eurasian Economic Union and in the Union State is considered. Examples of regulation in the regions of Russia of relations on the formation of a circular economy are given. Based on the conducted comparative analysis, it was revealed that the category of «green» economy is used in program and strategic documents, subordinate regulatory legal acts. At the same time, different terms «green economy», «green investments», «green financial instruments», «closed-cycle economy», «circular economy», «green energy», etc. are used. Conclusions. It seems appropriate to improve legislation in the field of regulation of relations connected with energy transition. It is advisable to adopt sectoral and regional plans for adaptation to climate change and energy transition. It is expedient to substantiate and develop proposals for the formation of a concept of legal regulation in the field of energy transition, including common approaches, principles of regulation of the «green» economy in terms of energy transition within the general policy of the EAEU member states and within the Union State.