Abstract: This article is dedicated to examination of the phenomenon of private military companies as a regional actor of security. Leaning on the analysis of international normative legal documents, the authors derive the definition of private military companies due to the fact that neither academic nor applied spheres have precise understanding of this phenomenon. The key research method is the structural and functional analysis, which allows authors considering the object of study from the perspective of various systems of actors. With the increased demand for private military services, private military companies gradually shift from the category of organizations serving military operations to the category of full-fledged independent military organizations that are capable of fulfilling the functions of regular army. For the past two decades, the market for private military services has grown from $ 55 billion to over $200 billion in 2010. The scientific novelty consists in comprehensive overview of various aspects and trends that take place in the market of private military services, as well as in classification of motives and consequences of usage of private military companies in armed missions. The authors discuss the question of international legal status of private military companies, provide practical examples of their activity with the prolonged consequences for regional systems of international relations, analyze the mechanisms of use of these companies in the current context, as well as synthesize the key factors of the increased demand for their services. The absence of regulation of the work of private military companies and ambiguous status of their employees in international law make it virtually impossible to impose international responsibility upon them.