Chinese medicine believes the etiology and pathogenesis of any given disease are the consequence of the struggle between the Righteous Qi and the pathogenic factors, where the weakened state of Righteous Qi cannot resist the attack of pathogenic factors, leading to the imbalance of yin and yang and the development of disease. The Yellow Emperor's Canon of Medicine teaches, “When the Righteous Qi is within, external pathogenic factors would not dare invade” and “if pathogenic factors invade the body, Qi in the body must be deficient”. In other words, a strong state of righteous qi (a healthy immune system) can protect against internal and external pathogenic factors, maintaining the healthy state of the body; however, when the righteous qi is in a weakened state (weakened or deficient immune system), the ability of the immune system to protect and maintain a healthy state is compromised, thus leading to disease. The functions of Righteous Qi in Chinese medicine can be summarized within the three main functions of the immune system: defense, homeostasis and surveillance. As acupuncture acts on the immune system via the intricate meridian-neuroendocrine immune network, it exerts important regulating effects on the immune system that leads towards the restoration of good health.