The meridian system consists of three parts: the principal meridians, the eight extra meridians and the twelve divergent meridians.

There are twelve principal meridians, e.g. the three yang meridians of the hand, the three yang meridians of the foot, the three yin meridians of the hand and the three yin meridians of the foot. Why they are called "twelve principal meridians"? It is because these meridians are the chief pathways of qi and blood. The twelve principal meridians start and terminate at given parts, run along regular routes and meet in a specified sequence. They are moreover, associate with the zang-fu organs.

There are also eight extra meridians: the Du (govern vessel), Ren(conception vessel), Chong, Dai, Yinqiao, Yangqiao, Yinwei, Yangwei meridians. The eight extra meridians interlace the twelve principal meridians, helping reinforce the communication between and adjustment of the twelve principal meridians. The eight extra meridians are not directly related to any of the internal organs.

The twelve divergent meridians are extensions of the twelve principal meridians. They usually start from the limbs, run deeper into the body and emerge from the body at the back of the neck. Again, these meridians have counterparts in both the left and right sides of the body. They are divided into yang and yin divergent meridians. The yang divergent meridians start from the six principal yang meridians, and, after traveling through the body, rejoin the principal meridians. They yin divergent meridians give off from the six yin principal meridians; however, after traveling through the body, the join the yang principal meridians with which they are externally and internally related.
　　 Among the meridians mentioned above, the twelve principal meridians and Du meridian (govern vessel meridian) as well as Ren meridian (conception vessel meridian) are very important parts in clinic. Therefore, we will mainly discuss these fourteen meridians in detail as follows.