Qin (CHIN, /tʃɪn/, or Ch'in) was an ancient Chinese state during the Zhou dynasty. It is traditionally dated to 897 BC. The state of Qin originated from a reconquest of western lands that had previously been lost to the Xirong. Its location at the western edge of Chinese civilisation allowed for expansion and development that was not available to its rivals in the North China Plain.

After extensive reform during the 4th century BC, Qin emerged as one of the dominant powers among the Seven Warring States. It unified the seven states of China under Qin Shi Huang in 221 BC. This unification established the Qin dynasty, which, despite its short duration, had a significant influence on later Chinese history. Accordingly, the state of Qin before the Qin dynasty was established is also referred to as the "predynastic Qin" or "proto-Qin".

According to the 2nd-century BC Records of the Grand Historian by Sima Qian, the state of Qin traced its origin to Zhuanxu, one of the legendary Five Emperors in ancient times. One of his descendants, Boyi, was granted the family name of Ying by Emperor Shun. During the Xia and Shang dynasties, the Ying clan split in two: a western branch that migrated across the Ordos Plateau to Quanqiu (犬丘; 'hill of the Quanrong', modern Li County, Gansu), and an eastern branch that settled east of the Yellow River in modern Shanxi. The latter became the ancestors of the rulers of the later state of Zhao.

The western Ying clan at Quanqiu were lords over the Xichui ('western march') region west of Mount Long and served as a buffer state for the Shang dynasty against invasions by the Xirong (also called Rong). One of the Shang, Elai, was killed defending King Zhou of Shang during the rebellion led by Ji Fa that established the Zhou dynasty. The Ying clan was, however, allied with the politically influential marquesses of Shen, whom the Zhou monarch relied upon heavily to manage the Rong people. The Ying clan was thus allowed to retain their lands and continued serving as an attached vassal under the Zhou dynasty. Feizi, a younger son of Elai's fourth-generation descendant Daluo, impressed King Xiao of Zhou so much with his horse breeding skills that he was awarded a separate fief in the valley of Qin (modern Qingshui and Zhangjiachuan in Gansu) northeast of Quanqiu, and his seat was named Qinyi (秦邑; Qin's hamlet) in the modern town of Qinting (秦亭). Both branches of the western Ying clan lived in the midst of the Rong tribes, sometimes fighting their armies and sometimes intermarrying with their kings.

Scholars Annette Juliano and Arthur Cotterel have suggested that having a horse-breeder as their ancestor may imply that the Ying family had a partial connection to nomadic tribes. As late as 266 BC, a noble of Wei remarked that they shared customs with the Rong and Beidi tribes. The Central Plains states seemed to hold Qin culture and that of other peripheral states like Yan and Chu in low regard, due to the marginal location of their states. Qin was the second state after Zhao to adopt cavalry tactics from the nomads. Following the collapse of the Zhou dynasty, the Qin state absorbed cultures from two of the Four Barbarians (Rong and Beidi) from the west and north, which made the other warring states view their culture with low esteem. The Qin state was sensitive to cultural discrimination by Central Plains states and attempted to assert their Huaxia identity. In Qin law, mixed-ethnicity offspring were categorised as Huaxia, and they had a preference for importing recruits from the neighbouring state of Jin.

In 842 BC, nobles revolted against the corrupt King Li of Zhou in a coup known as the 'countrymen's riot' (國人暴動). They overthrew him the following year, leading the country into political turmoil. The Xirong tribes seized this opportunity to rebel against the Zhou dynasty, attacking and exterminating the senior branch of the Ying clan at Quanqiu. This left the cadet branch at Qinyi as the only surviving branch of the Ying clan in the west.

After King Xuan of Zhou ascended to the throne in 827 BC, he appointed Qin Zhong, Feizi's great-grandson, as the commander of his forces in the campaign against the Xirong. In 822 BC, Qin Zhong was killed in battle and succeeded by his eldest son, Duke Zhuang. To commemorate Qin Zhong's loyalty, King Xuan summoned Duke Zhuang and his four younger brothers and gave them 7,000 soldiers. The Qin brothers successfully defeated the Rong and recovered their lost patrimony, formerly held by the deceased branch of the Ying clan. King Xuan formally awarded them the territory of Quanqiu. Duke Zhuang then moved his seat from Qinyi to Quanqiu and had three sons.

When Duke Zhuang died in 778 BC, his eldest son Shifu chose to continue fighting the Xirong and avenge their grandfather, turning down his place in the line of succession. As a result, his second son, Duke Xiang, ascended as the clan leader. In 777 BC, Duke Xiang arranged for his younger sister, Mu Ying, to marry a Rong leader named King Feng (豐王) in an apparent attempt to make peace. The following year, Duke Xiang moved the Qin capital eastward from Quanqiu to Qian (汧; modern Long County, Shaanxi). However, Quanqiu soon fell to the Rong again after he left. His older brother Shifu, who led the defense of Quanqiu, was captured by the Rong and was released a year later.