Acupuncture is a traditional Chinese medical technique for unblocking chi (ch'i or qi) by inserting needles at particular points on the body to balance the opposing forces of yin and yang. Chi is an energy that allegedly permeates all things. It is believed to flow through the body along 14 main pathways called meridians. When yin and yang are in harmony, chi flows freely within the body and a person is healthy. When a person is sick, diseased, or injured, there is an obstruction of chi along one of the meridians. Traditional Chinese medicine has identified some 500 specific points where needles are to be inserted for specific effects.

The WHO, the National Center for Complementary and Alternative Medicine (NCCAM) of the National Institutes of Health (NIH), the American Medical Association (AMA) and various government reports have all studied and commented on the efficacy of acupuncture. There is general agreement that acupuncture is safe when administered by well-trained practitioners using sterile needles.

Chinese medicine is based on a pre-scientific paradigm of medicine that developed over several thousand years. Its theory holds the following explanation of acupuncture:

Health is a condition of balance of yin and yang within the body. Particularly important in acupuncture is the free flow of Qi, a difficult-to-translate concept that pervades Chinese philosophy and is commonly translated as "vital energy"). Qi is immaterial and hence yang; its yin, material counterpart is Blood (capitalized to distinguish it from physiological blood, and very roughly equivalent to it). Acupuncture treatment regulates the flow of Qi and Blood, tonifying where there is deficiency, draining where there is excess, and promoting free flow where there is stagnation. An axiom of the medical literature of acupuncture is "no pain, no blockage; no blockage, no pain."

Many patients claim to experience the sensations of stimulus known in Chinese as de qi ("obtaining the Qi" or "arrival of the Qi"). This kind of sensation was historically considered to be evidence of effectively locating the desired point. (There are some electronic devices now available which will make a noise when what they have been programmed to describe as the "correct" acupuncture point is pressed).

TCM treats the human body as a whole that involves several "systems of function" generally named after anatomical organs but not directly associated with them. The Chinese term for these systems is Zang Fu, where zang is translated as "viscera" or solid organs and fu is translated as "bowels" or hollow organs. In order to distinguish systems of function from physical organs, Zang Fu are capitalized in English, thus Lung, Heart, Kidney, etc. Disease is understood as a loss of balance of Yin, Yang, Qi and Blood (which bears some resemblance to homeostasis). Treatment of disease is attempted by modifying the activity of one or more systems of function through the activity of needles, pressure, heat, etc. on sensitive parts of the body of small volume traditionally called "acupuncture points" in English, or "xue" (?, cavities) in Chinese. This is referred to in TCM as treating "patterns of disharmony.

Needles being inserted into a patient's skin.Most of the main acupuncture points are found on the "twelve main meridians" and two of the "eight extra meridians" (Du Mai and Ren Mai) a total of "fourteen channels", which are described in classical and traditional Chinese medical texts, as pathways through which Qi and "Blood" flow. There also exist "extra points" not belonging to any channel. Other tender points (known as "ashi points") may also be needled as they are believed to be where stagnation has gathered.

Treatment of acupuncture points may be performed along several layers of pathways, most commonly the twelve primary channels, or mai, located throughout the body. The first twelve channels correspond to systems of function: Lung, Large Intestine, Stomach, Spleen, Heart, Small Intestine, Bladder, Kidney, Pericardium, San Jiao (an intangible, also known as Triple Burner), Gall Bladder, and Liver. Other pathways include the Eight Extraordinary Pathways (Qi Jing Ba Mai), the Luo Vessels, the Divergents and the Sinew Channels. Ashi (tender) points are generally used for treatment of local pain.

Of the eight extraordinary pathways, only two have acupuncture points of their own: the Ren Mai and Du Mai, which are situated on the midline of the anterior and posterior aspects of the trunk and head respectively. The other six meridians are "activated" by using a master and couple point technique which involves needling the acupuncture points located on the twelve main meridians that correspond to the particular extraordinary pathway.

The twelve primary pathways run vertically, bilaterally, and symmetrically and every channel corresponds to and connects internally with one of the twelve Zang Fu ("organs"). This means that there are six yin and six yang channels. There are three yin and three yang channels on each arm, and three yin and three yang on each leg.

The three yin channels of the hand (Lung, Pericardium, and Heart) begin on the chest and travel along the inner surface (mostly the anterior portion) of the arm to the hand.
The three yang channels of the hand (Large intestine, San Jiao, and Small intestine) begin on the hand and travel along the outer surface (mostly the posterior portion) of the arm to the head.
The three yin channels of the foot (Spleen, Liver, and Kidney) begin on the foot and travel along the inner surface (mostly posterior and medial portion) of the leg to the chest or flank.
The three yang channels of the foot (Stomach, Gallbladder, and Urinary Bladder) begin on the face, in the region of the eye, and travel down the body and along the outer surface (mostly the anterior and lateral portion) of the leg to the foot.
The movement of Qi through each of the twelve channels comprises an internal and an external pathway. The external pathway is what is normally shown on an acupuncture chart and is relatively superficial. All of the acupuncture points of a channel lie on its external pathway. The internal pathways are the deep course of the channel where it enters the body cavities and related Zang Fu organs. The superficial pathways of the twelve channels describe three complete circuits of the body, chest to hands, hands to head, head to feet, feet to chest, etc.

The distribution of Qi through the pathways is said to be as follows (the based on the demarcations in TCM's Chinese Clock): Lung channel ofhand taiyin to Large Intestine channel of hand yangming to Stomach channel of foot yangming to Spleen channel of foot taiyin to Heart channel of hand shaoyin to Small Intestine channel of hand taiyang to Bladder channel of foot taiyang to Kidney channel of foot shaoyin to Pericardium channel of hand jueyin to San Jiao channel of hand shaoyang to Gallbladder channel of foot shaoyang to Liver channel of foot jueyin then back to the Lung channel of hand taiyin. According to the "Chinese clock", each channel occupies two hours, beginning with the Lung, 3AM-5AM, and coming full circle with the Liver 1AM-3AM.

Traditional diagnosis
The acupuncturist decides which points to treat by observing and questioning the patient in order to make a diagnosis according to the tradition which he or she utilizes. In TCM, there are four diagnostic methods: inspection, auscultation and olfaction, inquiring, and palpation.

Inspection focuses on the face and particularly on the tongue, including analysis of the tongue size, shape, tension, color and coating, and the absence or presence of teeth marks around the edge.
Auscultation and olfaction refer, respectively, to listening for particular sounds (such as wheezing) and attending to body odor.
Inquiring focuses on the "seven inquiries", which are: chills and fever; perspiration; appetite, thirst and taste; defecation and urination; pain; sleep; and menses and leukorrhea.
Palpation includes feeling the body for tender "ashi" points, and palpation of the left and right radial pulses at two levels of pressure (superficial and deep) and three positions Cun, Guan, Chi(immediately proximal to the wrist crease, and one and two fingers' breadth proximally, usually palpated with the index, middle and ring fingers).
Other forms of acupuncture employ additional diagnosic techniques. In many forms of classical Chinese acupuncture, as well as Japanese acupuncture, palpation of the muscles and the hara (abdomen) are central to diagnosis.

TCM perspective on treatment of disease
Although TCM is based on the treatment of "patterns of disharmony" rather than biomedical diagnoses, practitioners familiar with both systems have commented on relationships between the two. A given TCM pattern of disharmony may be reflected in a certain range of biomedical diagnoses: thus, the pattern called Deficiency of Spleen Qi could manifest as chronic fatigue, diarrhea or uterine prolapse. Likewise, a population of patients with a given biomedical diagnosis may have varying TCM patterns. These observations are encapsulated in the TCM aphorism "One disease, many patterns; one pattern, many diseases".

Classically, in clinical practice, acupuncture treatment is typically highly individualized and based on philosophical constructs as well as subjective and intuitive impressions, and not on controlled scientific research.