Zhao (traditional Chinese: 趙; simplified Chinese: 赵) was one of the seven major states during the Warring States period of ancient China. It emerged from the tripartite division of Jin, along with Han and Wei, in the 5th century BC. Zhao gained considerable strength from the military reforms initiated during the reign of King Wuling, but suffered a crushing defeat at the hands of Qin at the Battle of Changping. Its territory included areas in the modern provinces of Inner Mongolia, Hebei, Shanxi and Shaanxi. It bordered the states of Qin, Wei, and Yan, as well as various nomadic peoples including the Hu and Xiongnu. Its capital was Handan, in modern Hebei province.

Zhao was home to the administrative philosopher Shen Dao, Confucian Xun Kuang, and Gongsun Long, who is affiliated to the school of names.

The Zhao clan within Jin had been accumulating power for centuries, including annexing the Baidi state of Dai in the mid-5th century BC.

At the end of the Spring and Autumn period, Jin was divided between three powerful ministers, one of whom was Zhao Xiangzi, patriarch of the Zhao family. In 403 BC, the Zhou king formally recognised the existence of the Zhao state along with two other states, Han and Wei. Some historians, beginning with Sima Guang, take this recognition to mark the beginning of the Warring States period.

At the beginning of the Warring States period, Zhao was one of the weaker states. Despite its extensive territory, its northern border was frequently harassed by the Eastern Hu, Forest Hu, Loufan, Xiongnu, and other northern nomadic peoples. Zhao lacked the military might of Wei or the wealth of Qi, and became a pawn in the struggle between them. This struggle came to a head in 354 BC when Wei invaded Zhao, forcing Zhao to seek help from Qi. The resulting Battle of Guiling was a major victory for Qi, reducing the threat to Zhao's southern border.

Zhao remained relatively weak until the military reforms of King Wuling of Zhao (325–299 BC). Zhao soldiers were ordered to dress like their Hu neighbours and to replace war chariots with cavalry archers (胡服骑射; 胡服騎射; húfúqíshè). This reform proved to be a brilliant and pragmatic strategy. With the advanced technology of the Chinese states and tactics of the steppe nomads, Zhao's cavalry became a powerful force. As a result, the newly empowered Zhao were more evenly matched with their greatest threat, Qi.

Zhao demonstrated its increased military prowess by conquering the state of Zhongshan in 295 BC after a protracted war and annexing territory from the neighbouring states of Wei, Yan, and Qin. During this time, Zhao cavalry also occasionally intruded into Qi during latter campaigns against Chu.

Several brilliant military commanders of the period served Zhao contemporaneously, including Lian Po, Zhao She, and Li Mu. Lian Po was instrumental in defending Zhao against Qin. Zhao She was most active in the east, leading the invasion of Yan. Li Mu defended Zhao against the Xiongnu in the Zhao–Xiongnu War and later against Qin.