Theories defining public law and private law are analysed: principally interest theory, subjection theory and subject theory. Hence paper examines the international legal regulation of doping, considering that it has undergone a process from private law to public law. Paper presents Polish Law and particularly the Act on Combating Doping in Sport of 21 April 2011 which provides the legal basis for the existence of the Polish Anti-Doping Agency (POLADA) as a state legal entity. POLADA is a body governed by public law, which establishes anti-doping rules, controls, and oversees compliance, authorizes the use of prohibited substances or methods, and conducts disciplinary action for violation of anti-doping rules.