Like yoga, Tai Chi is a movement modality, but it differs from yoga in that no mat is used, and it is taught in a class with everyone standing arranged in rows and columns. Loose clothing and flat soled shoes are usually used. Tai Chi (taiji) is a shortened version of t'ai chi ch'üan. Taiji refers to the philosophy of the forces of yin and yang, related to the moves.  Chang San-Feng who lived 1391-1459 is credited with the origin of Tai Chi, and created the 13 postures, adopted from Chinese martial arts. Later, Wang Chun-Yuel created the continuous movement that is used in Tai Chi.  Many different schools of Tai Chi later developed. Tàijíquán training involves five elements, taolu (solo hand and weapons routines/forms), neigong and qigong (breathing, movement and awareness exercises and meditation), tuishou (response drills) and sanshou (self defence techniques). While tàijíquán is typified by some for its slow movements, many styles (including the three most popular: Yang, Wuand Chen) have secondary forms with faster pace. Some traditional schools teach partner exercises known as tuishou("pushing hands"), and martial applications of the postures of different forms (taolu). There are now 5 major styles of Tai chi listed in order of popularity: Yang, Wu, Chen, Sun and Wu/Hao.  In the US, Tai chi is primarily used for its exercise capabilities rather than for sport or for defense. 

Tai Chi Qigong for osteoarthritis demonstrated significant improvement for quality of life (Grade B), pain relief (Grade C+) and physical function (Grade C+). Sun style Tai Chi gave significant improvement for pain relief (Grade B) and physical function (Grade B)  (Clin Rehabil. 2017 May;31(5):582-595).  Tai chi reduces the risk of falls in the elderly by 50% (J Am Geriatr Soc. 2017 Sep;65(9):2037-2043).  Other evidence for the benefits of tai chi: Excellent evidence in the treatment of osteoarthritis, Parkinson disease, rehabilitation for chronic obstructive pulmonary disease, and improving cognitive capacity in older adults. There is good evidence of benefit for depression, cardiac and stroke rehabilitation, and dementia. There is fair evidence of benefit for improving quality of life for cancer patients, fibromyalgia, hypertension, and osteoporosis. (Can Fam Physician. 2016 Nov;62(11):881-890).