In the present paper

the authors discuss the theory of the collateral system of meridians and collateral diseases from ① the pose of the concept of “collateral system and collateral diseases"; ② the component of the collateral system; ③ functions of the collateral system; ④ pathology of the collateral system; and ⑤ clinical application of the theory of the collateral system and collateral disorders. The collateral system is composed of fifteen major collaterals

yin and yang collaterals

minute collaterals

superficial collaterals

etc. and is the basic functional unit for transporting qi and blood

communicating the zangfu organs and the body surface

and regulating physiological activities of the human body. The collateral diseases are those functional disorders of the body caused by various factors induced blockage of the collateral branches of meridians and dysfunctions of circulation of qi

blood and body fluid. The deep research on the theory of the collateral system and collateral diseases will help us a lot in carrying forward and developing traditional theories of Chinese medicine

gaining a clear idea about the essence of the doctrines of zangfu organs and meridian collaterals

understanding the pathogenesis of different diseases

and in making correct diagnosis and treatment of various disorders according to the comprehensive analysis on the symptoms and signs.