What is the difference between Qi Gong and Tai Chi?

I have done Qi (CHI) Gong videos and I really enjoyed them. I found them energizing and peaceful. The Community College here is offering a summer Tai Chi class and the two seem pretty much the same to me. Can anyone tell me the differences between these two?|||You might like Tai Chi. It takes longer to learn than Qi Gong, but it has the same mental and physical benefits as far as easing pain and increasing mobility. During the weeks that it takes to learn a short form, I get quite a workout because I am repeatedly practicing moves that may not be an exertion if I only do it once, but repeating it for an hour in the course of trying to remember it, I really start to feel the burn!|||Often t'ai chi classes will incorporate qi gong in their teaching, so you are right that there are similarities. T'ai chi is a martial art though, so if you take a t'ai chi class you can expect to learn some qi gong, t'ai chi forms (a set series of movements, kind of like katas in other martial arts), the martial applications of the movements in those forms (which are not always obvious), and push hands. Definitely give it a try!