There are five main styles: the Yang, Wu, Chen, Hao and combination styles. The Chen is the original style, established in central China's Chen village in the seventeenth century. It is the most athletic and physically difficult style, incorporating jumping kicks and stamping actions. The Yang style, which has many variations, originated from the Chen and is the most widely practiced style of tai chi today. The Wu style, which was developed directly from the Yang, is the second most popular style. It emphasizes smaller, more compact movement than the Yang and incorporates more internal chi work. The Hao style is very rare, even in China. It is very internal and has the smallest and most subtle movements. Combination styles mix various styles together, including movements from other martial arts.
Many of these styles have long, medium and short sets of movements, which are known as "forms." Short forms are the best for beginners. For more details on choosing a tai chi style, see The Big Book of Tai Chi, chapter 9. Bruce Frantzis has extensive training in the Yang, Wu, Chen and Chen Pan Ling combination styles. However, he primarily teaches Wu style tai chi, as he has found this style to be the best for health and meditation.
A must read for those who are new to qigong, those who are already practitioners, and anyone interested in complementary medicine or self-help.