the diverse body of medical theory and practice that has evolved in China, comprising four branches: acupuncture and moxibustion, herbal medicine, qi gong, and tui na. Although TCM encompasses a variety of theory and practice, all of its forms share certain underlying characteristics. The body and mind are considered together as a dynamic system subject to cycles of change and affected by the environment, and emphasis is on supporting the body's self-healing ability. Fundamental to TCM are the yin-yang principle and the concept of basic substances that pervade the body: qi, jing (essence), and shen (spirit), collectively known as the three treasures, and the blood (a fluid and material manifestation of qi) and body fluids (which moisten and lubricate the body). Disease arises from a disturbance of qi within the body, the particular pathological process depending on the location of the disturbance; causes are classified into three groups, external (which are environmental), internal (emotions), and miscellaneous (such as diet, fatigue, or trauma). Diagnosis is by visual assessment, listening and smelling, questioning, and palpation; a single biomedical disease may be associated with a large number of TCM diagnoses, and one TCM diagnosis may encompass a number of biomedical diseases. Once a diagnosis is established, therapy aims at restoring the body's homeostasis by treating the root cause of the disease.