In pre-historic times, the Chinese discovered that there were certain points of the body, which if massaged, punctured, heated or burned, relieved pain or had a beneficial effect on certain disorders.  Through the passage of time, many such points were discovered and it was found that by the stimulation of widely separated points it was possible to influence  the functioning of a specific internal Organ.  These points were then systematically arranged on the basis of the pertaining Organ, over which it was perceived they had an influence.  The series of points which had an effect on a particular Organ were connected to form a Channel.  This is the basis of the theory of Jing-Luo, leading in time, to the finely evolved system of causal interrelationships between points in a Channel, and between the Channels themselves, which were described in the ancient classic, Huang Di Nei Jing.

     There are twelve Regular Channels, called the Twelve Paired Channels, and eight extra Channels, called the Eight Extraordinary Channels.

     Each of the Twelve paired Channels, relates to one of the twelve internal Organs.  Like the internal Organs, therefore, six Channels are Yin and six are Yang.  The Yin and Yang Channels, thus, follow the coupling of the Zang and Fu* Organs and, for this reason, they are referred to as Paired Channels and are said to have an "interior-exterior relationship" with each other.  Because of other direct connections to the twelve internal Organs, they are also called the Organ Channels, and the Channel is named after the Organ to which it is connected.  *Zang=Solid organs; Fu=Hollow organs.  In Chinese Zang=to store, Fu=to receive.

     Of the eight Extraordinary Channels, two run on the midline, one in front (the Ren Channel) and the other in the back (the Du Channel).  These two Channels have their own acupuncture points.  The other six Extraordinary Channels do not have their separate points, but are formed by the interconnection of points of the Twelve Paired Channels and the Two Midline Channels.  The Eight  Extraordinary Channels are not connected to any pertaining Organ.

     Since only the Ren and Du Channels of the Eight Extraordinary Channels possess their own points, they are regularly used like the Twelve Paired Channels and together they are known as "the Fourteen Channels".

     This network of Channels connects the internal Organs and the exterior of man, the microcosm, with the Universe, the macrocosm, to establish a Universal Harmony.  For example, when the body is attacked by such external factors as wind, cold, heat, humidity, dryness and fire (also called "exogenous factors"), disease may be caused as these factors affect the balance of Qi (vital energy, pronounced "chee") in their pertaining Organs.  On the other hand, disease may be caused by emotional factors such as joy, anger, melancholy, obsession, sorrow, horror, surprise and shock (called "endogenous factors").  These diseases first occur in the internal Organs and then affect the Channels via the connections of the internal Organ with the Channels.  The ancient Chinese discovered that is was possible to cause a change in the body by skillfully influencing the Qi at the surface level, and this is the prime objective of acupuncture therapy.

     Modern scientists puzzle why acupuncture points exist on the body surface.  They were certainly not evolved for acupuncturists to insert needles!  According to some modern workers the points, probably, form "windows" on the body surface for exchange of cosmic energies, so that the body can remain in energy balance with the rest of the Universe (Macrocosm).

     Of the Twelve Paired Channels, six traverse the arm.  Of the six Channels serving the arm, three are Yin and run on the anterior aspect of the upper limb centrifugally, "The Three Yin Channels of Hand"; three are Yang and run centripetally on the posterior aspect of the upper limb, "The Three Yang Channels of Hand".  Likewise, of the six Channels serving the lower limb, three are Yin and run centripetally on the medial aspect of the leg, "The Three Yin Channels of Foot"; three are Yang and run centrifugally on the anterior, lateral, and posterior aspects of the lower limb, "The Three Yang Channels of Foot".

     The Three Yin Channels of Hand commence from the chest and flow to the Hand where they meet with the Three Yang Channels of Hand near the nails.

     The Three Yang Channels of Hand commence from the hand, ascend to the head where they meet three Yang Channels of Foot.

     The Three Yang Channels of Foot commence from the head, run towards to foot and there meet the three Yin Channels of foot.

     The Three Yin Channels of Foot commence from the foot, ascend to the chest and meet the three Yin Channels of Hand.

     A change of polarity of energy takes place from Yin to Yang at the wrist, and vice-versa at the ankle.

     When a standing man raises his hands above his head and worships the father, the sun above in heaven the originator of all Yang energy, then the Yang energy of heaven flows (to the Yin of the mother earth) via the "outer" side of his upper and lower limbs.  The Yin energy ascends in the reverse direction from the earth to the heaven above on the "inner" side of his limbs, thus, completing the macrocosm circulation.  Man is the son of heaven and earth. 

     All Organs above the diaphragm are Yin.  These are the Lung, Heart and Pericardium.**  They are connected to the three Yin Channels of Hand.  All solid Organs below the diaphragm are Yin.  These are the Spleen, Kidney*** and Liver.  They are connected to the Three Yin Channels of Foot.

     Of the Yang Organs, three are connected to the Three Yang Channels of Hand.  These are the Large Intestine, the Small Intestine, and Sanjiao (or the Three Body Cavities).  The other three Yang Organs are connected to the Three Yang Channels of Foot.  These are the Stomach, Urinary Bladder and the Gall Bladder.

     **Pericardium is the protector of the Heart.  Functionally, they form one Internal Organ.

    ***The Kidney has a Yin and a Yang aspect.