Mixed martial arts (MMA) is the combat sport in which two competitors attempt to achieve dominance over one another by utilizing a wide variety of permitted martial arts techniques. These techniques generally fall into three categories: striking (punches and elbows, kicks and knees), grappling (clinchs, takedowns and throws, ground fighting), and finishing holds (joint-locks, chokeholds). Victory is normally gained through knock-out, submission (one fighter concedes victory to the other by tapping the mat or his opponent with his hand), or stoppage by the referee, the fight doctor or a competitor's cornerman. Previously MMA was also known as "NHB" for "No Holds Barred", but this term is now technically retired; it is no longer an accurate description of the modern competitions which utilize a list of rules necessary for the fighters' safety.

MMA is also used to describe any hybrid style of martial arts which incorporate techniques and theories from several different martial arts. This especially applies to MMA styles which incorporate a mixture of ground fighting, stand-up striking, and takedowns in their training. However, hybrid martial arts are not addressed here, only MMA as a "realistic, few rules full contact fight sport".

As a result of these sporting events, martial arts training and the understanding of the combat effectiveness of various strategies have changed dramatically over the last ten years. While the early years included the widest possible variety of styles (everything from sumo to karate), modern fighters often train in a mixture of only three styles: amateur wrestling (focusing on clinches and takedowns and position dominance), submission wrestling (Brazilian Jiu Jitsu, Judo, Sambo) (focusing on submissions and positioning on the ground), and kickboxing (Muay Thai) and/or boxing (focusing on striking). These three distinct styles coincide with the "phases of combat" theory, which suggests that fights can be broken into three distinct phases, each requiring completely different skill sets: stand-up fighting, clinch fighting, and ground fighting. According to the theory, a fighter's best strategy is to determine the phase in which he has the greatest advantage over his opponent and then to influence the fight to take place in that phase.

Some well-known MMA organizations are the Ultimate Fighting Championship, Pride Fighting Championships.