Acupuncture is a system of healing that dates back thousands of years. At the core of Chinese medicine is the notion that a type of life force, or energy, known as Qi (pronounced "chee") flows through pathways (meridians) in the body. Each meridian corresponds to one organ, or group of organs, that governs particular bodily functions. Achieving the proper flow of Qi creates health and wellness. Qi maintains the dynamic balance of energy in the body. Yin and Yang, which are complementary opposites, is a foundational premise of Chinese philosophy and medicine. According to Chinese medicine, everything in nature has both yin and yang. When these forces are in balance, harmony is created and good health is maintained. An imbalance of Qi (too much, too little, or blocked flow) causes disease. To restore balance to the Qi- and thus to the body-, an acupuncturist inserts very thin, sterile, single-use needles at points along the meridians. These acupuncture points are places where the energy pathways are close to the surface of the skin.