I bought these videos separately. They do not have to be used together, and using only one does not in any way diminish the effectiveness. These videos have been a key component in my stress reduction program. They work better for me than Yoga because you are actively moving with control throughout the routines, which I find keeps my mind from being able to dwell on whatever is stressing me. By the end of each tape, I feel relaxed, centered, and balanced (which is quite an accomplishment!). Both instructors have pleasing voices and demeanors. It does help if you have at least a little previous experience with either Tai Chi or Chi Kung, but it is not strictly necessary. Another advantage is that you can perform these routines in a limited amount of space. Excellent production values and soothing music in a tranquil setting.