Yin is the darker element; it is passive, dark, moist, receptive, earthy, feminine, downward-seeking, and corresponds to the night (Chinese: 陰/阴; pinyin: yīn; literally "shady place, north slope (hill), south bank (river); cloudy, overcast").

Yang is the brighter element; it is active, light, dry, masculine, heavenly, upward-seeking and corresponds to the day (陽/阳; yáng; "sunny place, south slope (hill), north bank (river); sunshine").

Yin is often symbolized by water or earth, while Yang is symbolized by fire, or wind.

There is always an element of yang within yin and an element of yin within yang. Most forces in nature can be seen as having Yin and Yang states, and the two are usually in movement rather than held in absolute stasis.

Chinese philosophers stressed the importance of balance between the two to ensure social and political harmony. Rebellion, floods, and disease were said to be caused by an imbalance of yin and yang.

One of the best known presentations and applications of the concepts of yin and yang is found in the I Ching, the Chinese "Book of Changes;" the oldest Chinese classic text. The I Ching, which has long been used as an oracle, is a set of predictions represented by a set of 64 abstract line arrangements called hexagrams (卦 guà). Each line is either Yang (an unbroken, or solid line), or Yin (broken, an open line with a gap in the center). The I Ching was at the heart of Chinese thought, serving as a common ground for the Confucian and Taoist schools. In modern western society, the I Ching has become a popular source of profound wisdom and inspiration.