I just returned from Seoul, Korea. It is my second home. TKD is obviously the most prevelant art, however, cross training is very common. My instructors belong to the Soong Moo Kwan under GM Yi Jung Moon. They teach HKD, TKD, and Haedong Kumdo. Each instructor normally specialized in one art and cross trained in the others. Some specialized in all three. Korean Martial Arts Dojang