The principle of separation of powers implies the division of state power, which is uni�ied by its source, into three mutually independent branches. Each of the branches of power is responsible for an important area of state activity and, at the same time, exercises control over the conduct of activities within the authority of other branches of power, which is ensured by the mechanism of "checks and balances." In this regard, the analysis of some theoretical issues related to the history of the formation and development of the theory of separation of powers will serve to proper understanding of the content and essence of this principle and determine its place in the organization of effective state power. Consequently, the original ideas that form the core of the theory of separation of powers appeared in the political and legal thought of the ancient world, which was re�ined over the centuries and later formed into a uni�ied theory. John Locke and Montesquieu are recognized as the founders of this theory. Despite the fact that this theory was created quite a long time ago and has already been established as a principle of the formation of state power, disputes about the origin of this principle, its content, and its meaning in scienti�ic communities do not stop; the views are quite contradictory. The article analyzes some aspects of these issues from the point of view of the theory of state and law.