Traditional Chinese Medicine (also referred to as, TCM) and Acupuncture originated in China close to 5000 years ago. TCM and Acupuncture view the body as a whole and is based on balance, energy and harmony. It is based on the belief that illness and disease occur when there is a blockage or imbalance of Qi (life force energy) within the body. When blockages or imbalances do occur then a person is likely to experience chronic pain and a range of various illnesses.
Yin and Yang is also a part of Chinese Medicine and Acupuncture. It illustrates polarity and the notion that one cannot exist without the other. The two forces are opposites and yet complementary. In TCM illness is believed to be caused by an imbalance of Yin and Yang in the body. In an excess of Yin, the Yang Qi would be damaged therefore leading to the development of a cold disease. On the other hand excess Yang will likewise cause damage to the Yin Qi and lead to a heat disease being developed. As the balance is restored within the body so is the person's health. Here is a graphic to help give you a better understanding of the two opposing forces referred to as Yin and Yang.
TCM and Acupuncture also refer to the five elements as part of its theory. The five elements symbolically represent the stages of human life and explain the functioning of the body. The five elements are: metal, wood, water, fire and earth. Each element supports the others, thus maintaining a balance within the body. Here is an image explaining the five elements and their connection with one another.