A taijitu (simplified Chinese: 太极图; traditional Chinese: 太極圖; pinyin: tàijítú; Wade–Giles: t'ai⁴chi²t'u²) is a symbol or diagram (图 tú) in Chinese philosophy representing Taiji (太极 tàijí "great pole" or "supreme ultimate") representing both its monist (wuji) and its dualist (yin and yang) aspects. Such a diagram was first introduced by Song Dynasty philosopher Zhou Dunyi (周敦頤 1017–1073) in his Taijitu shuo 太極圖說.
The modern Taoist canon, compiled during the Ming era, has at least half a dozen variants of such taijitu. The two most similar are the "Taiji Primal Heaven" (太極先天圖 tàijí xiāntiān tú) and the "wuji" (無極圖 wújí tú) diagrams, both of which have been extensively studied during the Qing period for their possible connection with Zhou Dunyi's taijitu.
Ming period author Lai Zhide (1525–1604) simplified the taijitu to a design of two interlocking spirals. In the Ming era, the combination of the two interlocking spirals of the taijitu with two black-and-white dots superimposed on them became identified with the He tu or "Yellow River diagram" (河圖). This version was reported in Western literature of the late 19th century as the "Great Monad", and has been widely popularised in Western popular culture as the "yin-yang symbol" since the 1960s. The contemporary Chinese term for the modern symbol is 太极兩儀图 "two-part Taiji diagram".