The research deals with the subject of energy service contract. The aim of the research is to identify the elements of the contract subject and their characteristics. The research is based on the following methods: formal legal method and general analysis and synthesis. The research results include the author's definition of the subject of the energy service contract, as well as the description of the subject elements and their characteristics. The research output can be used in legal practice. It can also be implemented while developing the educational courses in the field of energy efficiency and further legal research.