Jeet Kune Do

Referred to as the "formless form", its greatest strength is its unpredictability, as most fighting styles teach you to fight against someone trained in the same style. (With the possible exceptions of judo and aikido.) Thus, you are trained to expect certain punches, blocks, etc. Jeet Kune Do takes advantage of those expectations.

Bruce Lee's style of martial art is actually not strictly a style at all.

In his book The Tao of Jeet Kune Do he is quite insistent about this point, citing that one of the problems with styles of martial arts was their inflexibility. Bruce Lee was more concerned with what was practical and effective than what was traditionally part of any style of martial art. "Jeet Kune Do" was just a convenient name with which to label his sytem of approaching combat.

Jeet kune do is not a style per se, more of a philosophy, true, but there is definitely a physical foundation of theories and tools which Bruce Lee drew upon to create his art. These were: Boxing, the trapping aspects of Wing Chun, and the footwork, theory, and strategy of western fencing. He also utilized kicking technique from the french art of savate (that kick he does in Return/Way of the dragon where the guy with the kicking shield goes flying into the cardboard boxes, that's a savate kick.) and took grappling techniques from judo and wrestling. (NOT brazilian jiu jitsu, which is where all the modern jkd people get their ground game.)

However it is also worth noting that Bruce shut down his schools because he felt the individual must learn for him/her self; having 'truth' sold to you is a false truth. It is more valuable when you discover it for yourself.

Basically he felt martial artists, the true JKD men, should seek the truth on their own through experimentation and controlled sparring. If someone else is teaching you a system, even if it's called jeet kune do, you will only be able to express that system. It's like the difference between playing perfectly someone else's symphony, or playing free-form jazz. Jeet kune do is the jazz of martial arts.