This is the fastest growing sport in America, and arguably, many parts of the world.
As the name suggests, any fighter from any style can compete. Nowadays, though, it's considered taboo to even dream of competing without having both a strong standup/striking base(ex. karate, kickboxing, etc...), but
also a strong ground fighting base(ex. Greco-Roman wrestling, catch wrestling, BJJ, Judo, etc...).
This is because you'd be surprised at how ineffective many standup techniques are when you actually have to worry about being taken down or thrown to the ground.
Currently, the largest MMA organization is UFC(
www.ufc.com), which bought out it's rival from Japan, PrideFC, and has put together some of the matchups that all fans have wanted to see.
I actually didn't get into MMA myself until I started BJJ, where my trainer likes to chat it up about MMA all the time before/after class and during warmups.
Anyone else here fans?