In traditional Chinese culture and the East Asian cultural sphere, qi, also ki or chi in Wade–Giles romanization ( CHEE qì), is believed to be a vital force forming part of any living entity. Literally meaning "vapor", "air", or "breath", the word qi is often translated as "vital energy", "vital force", "material energy", or simply as "energy". Qi is the central underlying principle in Chinese traditional medicine and in Chinese martial arts. The practice of cultivating and balancing qi is called qigong.

Believers in qi describe it as a vital force, the flow of which must be unimpeded for health. Qi is a pseudoscientific, unverified concept, and is unrelated to the concept of energy used in science (vital energy itself being an abandoned scientific notion). The historian of medicine in China Paul U. Unschuld adds that there "is no evidence of a concept of 'energy' – either in the strictly physical sense or even in the more colloquial sense – anywhere in Chinese medical theory."