The paper addresses possible approaches to and challenges with providing statutory definition of “conflict of interest”. Based on the analysis of legislation in more than 20 countries as well as relevant documents of international organizations, three widely used models for defining conflict of interest are identified and their comparative advantages and disadvantages are considered. In addition, certain elements of the conflict of interest definition that can have a significant impact on law enforcement practice are discussed in detail. Special attention is paid to the history of the development of relevant legislation in Russia, the problems of the existing definition as well as feasible directions for its improvement.