In this article there are considered current views on biology of ovarian serous borderline tumors, there is presented a modern histological classification of 2014, which has undergone some changes. Variants of serous borderline tumors are described in terms of morphology, clinical course and prognosis. Also there is discussed the issue of the pathogenesis in the development of ovarian borderline tumors, the contribution of gene mutations in the occurrence of borderline, poorly or well differentiated ovarian tumors. There are described in details features of morphology of serous borderline tumors, the interrelationship of their occurrence and dedifferentiation in dependence on the molecular and genetic deteriorations. In the article there is considered the microinvasive version of the serous borderline tumors and specified criteria for the establishment of this diagnosis. There are given the definition and characterization of micropapillary serous borderline tumors, there is discussed their impact on the course of the disease and prognosis. The issue of terminology is considered in terms of current views and history.