The theory of Zangfu is a collective name for the various Yin and Yang organs identified in TCM. A Yin organ is called a Zang and a Yang organ is called a Fu. Each organ is considered to have its own functions, but these functions have a far wider scope than the purely physiological function described in Western medicine.

The Zang consists of the five solid organs -- spleen, heart, lungs, liver, and kidneys.

The Fu consists of the six hollow organs -- small intestine, large intestine, gall bladder, bladder, stomach, and san jiao (a three-part invisible metabolizing organ in TCM concept).

The meridian (energy channels) theory is the study of the physiological function and pathological change on the meridians and their related zangfu organs. The essential functions of the meridian system are to "transport qi (energy force) and blood," "to maintain conductivity," and "to resist invasion of exogenous pathogenic factors (such as viruses)."