Historical development of the concept of mixed states from the times of its creation by E. Kraepelin till the modern unified criteria of bipolar mixed states establishment, which passed through a number of the outlined stages, is reviewed in the article. Critical evaluations of the official classifications currently accepted demonstrate their restrictive character. Results obtained for the development of a new more specific set of diagnostic criteria for mixed states are presented. Though the Kraepelin's definition of mixed states is still relevant, the article notes the tendency to conceptualize mixed states broadly and dimensionally. Preliminary proposals for the new classification DSM-V diagnostic system are reviewed and supposed contentious clauses of the difficulties in the development of a future edition of DSM-5 as well as ICD-11 are mentioned.