Two main issues are considered in this article. The first is the changing historical and legal status of private military companies (PMCs). Emerging after the end of World War II, the PMC phenomenon became well-established by the mid-1990s. In the first decade of the 21st century, PMCs not only engaged in military activity in different regions of the world but also participated as independent economic actors capable of occupying a certain niche in the military segment of the world economy. Following this review, the article examines the practical activities of PMCs drawing on the example of the conflict in Ukraine during the civil war that began there after the coup d’etat of February 2014 and which saw the removal of the legally elected president V. Yanukovych and the rise of nationalist radicals to power. It should be noted that the Ukrainian crisis is only one of many examples of the use of PMCs. Moreover, as demonstrated in this study, the most powerful PMCs in the world are represented in the territory of Ukraine, pointing to the extreme importance of the processes occurring in Ukraine from the view point of the interests of the dominant actors in the modern international system involved in Ukrainian affairs.