Some MMA groups have formed networks so they can exchange fighters. For example, the World Wide Cage Network includes the following organizations: * Cage Force (formerly Demolition of Octagon Gear, Japan) * Cage Warriors (UK) * Nordic Events Fight sport Promotions (Finland) * Warrior’s Realm (Australia) * Pangea Fights (California, USA) * Rumble on the Rock (Hawaii, USA) Zuffa owns both UFC and WEC as well as the Japan-based Pride Fighting Championships, so I would suspect that fighters in these three groups can slip from one organization to another quite easily. There are several international organizations that regulate MMA, and several in the US also. Zuffa is covered by rules originally established by the New Jersey Athletic Control Board. The “Unified Rules of Mixed Martial Arts” that New Jersey established has been adopted in other states that regulate mixed martial arts, including Nevada, Louisiana, and California. These rules are also used by many other promotions within the United States, becoming mandatory for those states that have adopted the rules, and so have become the standard de facto set of rules for professional mixed martial arts across the country. Zuffa, based in Las Vegas, adheres to these rules as adopted by the Nevada State Athletic Commission.