The work addresses the legal and practical issues of decentralized energy supply through or with the support of specialized companies, often referred to as contracting. It discusses the practical legal questions surrounding decentralized energy supply for industrial enterprises, commercial properties, and residential buildings, whether provided by the user themselves or by a contracted energy service provider. The generation of heat, cold, electricity, etc., is examined. The provision of such energy services is a complex and legally multifaceted task in practical implementation. From initial heat supply concepts, a diverse market for energy services has now developed. At the same time, this has also increased the need for legal clarification in various areas such as contract law, energy industry law, and tenancy law.