Taegeuk (Korean: 태극; Hanja: 太極, Korean pronunciation: [tʰɛgɯk̚]) is a Sino-Korean term meaning "supreme ultimate", although it can also be translated as "great polarity / duality / extremes". The term and its overall concept is derived from the Chinese Taiji, popularised in the west as the Yin and Yang. The symbol was chosen for the design of the Korean national flag in the 1880s. It substitutes the black and white color scheme often seen in most taijitu illustrations with blue and red, respectively, along with a horizontal separator, as opposed to vertical.

South Koreans commonly refer to their national flag as taegeuk-gi (태극기), where gi (기) means "flag" or "banner". This particular color-themed taegeuk symbol is typically associated with Korean traditions and represents balance in the universe; the red half represents positive cosmic forces, and the blue half represents the complementary or opposing, negative cosmic forces. It is also used in Korean shamanism, Confucianism, Taoism, and Buddhism.

The taegeuk diagram has been existent for the majority of written Korean history. The origins of the interlocking-sinusoid design in Korea can be traced to as early as the Goguryeo or Silla period, e.g. in the decoration of a sword, dated to the 5th or 6th century, recovered from the grave of Michu of Silla, or an artifact with the taegeuk pattern of similar age found in the Bogam-ri tombs of Baekje at Naju, South Jeolla Province in 2008. In the compound of Gameunsa, a temple built in AD 628 during the reign of King Jinpyeong of Silla, a stone object, perhaps the foundation of a pagoda, is carved with the taegeuk design.

Although some theories suggest that the Yin and Yang philosophy from early Chinese civilization may have influenced Gojoseon, there is currently no direct archaeological evidence linking the Taegeuk design itself to this period. Instead, the earliest known artifacts with recognizable Taegeuk or interlocking spiral motifs have been found in the Goguryeo, Baekje, and Silla kingdoms, dating from the 5th to 7th centuries. These findings indicate that the Taegeuk motif may have developed independently within the Korean cultural sphere.

Today the taegeuk is usually associated with Korean tradition and represents balance in the universe, as mentioned in the previous section (red is 양; yang, or positive cosmic forces, and blue is 음; eum, or negative cosmic forces). Among its many religious connotations (Korean Confucianism; Taoism in Korea; Korean Buddhism), the taegeuk is also present in Korean shamanism.

The taegeuk symbol is most prominently displayed in the center of South Korea's national flag, called the Taegeukgi, literally taegeuk flag (along with four of the eight trigrams used in divination). Because of the Taegeuk's association with the national flag, it is often used as a patriotic symbol, as are the colors red, blue, and black.

Though the taegeuk and the trigrams have been used since the earliest periods of Korean history, its use had started earlier in China.

The taegeuk is a Taoist icon which symbolizes cosmic balance, and represents the constant interaction between the yin and yang, also known as eum/yang (Korean: 음양; Hanja: 陰陽). The taegeuk symbol used on the flag originated from the Chinese Confucian classic known as The Book of Changes (also known as I Ching or Yijing), a book developed for use in divination.