The Professional Fighters League (PFL) is an American mixed martial arts league founded by venture capitalist Donn Davis in 2017 and launched in 2018, following the acquisition and restructuring of the former World Series of Fighting (WSOF) promotion in 2017 by MMAX Investment Partners. It is the first major MMA organization in which individual athletes compete in a regular season, post-season and championship, rather than on a year-round basis.

Most rule sets for mixed martial arts (MMA) competitions have evolved since the early days of Vale Tudo. As a result of health, legal, and moral concerns, many different rulesets were created, which give different countries and promotions very different tactics and strategies. Similarly, shoot wrestling organizations, such as Shooto, expanded their rulesets to integrate elements of Vale Tudo into their sport. However, for the most part, fighters accustomed to one rule set can easily acclimate to the others.