The author studies the specific features of formation of cluster structures, which allow to identify economic and social preconditions for the emergence and development of cluster relations. The development of any cluster formation should be viewed as the process of interaction between opposite sides and trends arising from the intrinsic characteristics of these opposites. The author considers that cluster relations should be viewed as a system of relations on the formation and use of all types of resources aimed at the implementation of the expanded reproduction with the purpose of receiving profits systematically. Under present conditions the development of cluster relations occurs with participation of actors of economic ensuring of cluster formations' activity. On the basis of a systematic approach the author identifies and structures internal and external economic and financial conditions and factors of cluster relations. Cluster development theory is complemented by justification of key features and economic elements of cluster relations. The justification of the economic essence of cluster relations is provided.