Economists use it to study the stock market.
Physicists use it to describe various natural phenomenon.
Chaos theory has even entered the average home. Washing machines are designed using chaos theory in order to provide a more thorough cleaning. I found the relationship between chaos theory and music to be particularly interesting. Music is often studied scientifically, either mathematically or physically. In the 1970's, two scientists, Richard Voss and John Clarke from the University of California, discovered that music could be formed algorithmically.