The majority of studies on Tai Chi conducted between 1996 and 2004 had focused on health and well being of Tai Chi exercise for senior adults. The results show that Tai Chi may lead to improved balance, reduced fear of falling, increased strength, increased functional mobility, greater flexibility, and increased psychological well-being, sleep enhancement for sleep disturbed elderly individuals, and increased cardio functioning. Wang, Collet, and Lau did a systematic review on Tai Chi research and found some limitations or biases existing in some of the studies, and it was difficult to draw firm conclusions about the benefits reported. Therefore, more well-designed studies are needed in the future. There need to be studies on the effects on younger and middle-aged people. More longitudinal studies are needed, since time is an important factor of physical and psychological interventions. Studies on the effects of Tai Chi on the immune system and bone loss reduction are still very exploratory and will be especially useful for arthritis patients and others with immune disorders. Future studies should investigate outcomes associated with Tai Chi training as a function of different instructional techniques, different Tai Chi styles, different diagnostic groups, and different age groups. It is not yet clear which of the components in Tai Chi makes the exercise form especially effective for seniors. Tai Chi exercise is a relatively "low tech" approach to preventing disability and maintaining physical performance in older adults. The positive effects of Tai Chi may be due solely to its relaxing, meditative aspects. The current data suggest that Tai Chi can influence older individuals' functioning and well being and provide some appreciation for why this exercise form has been practiced by older Chinese for more than 3 centuries.