Zhou Pingwang 周平王 (r. 770-720 BCE), King Ping of Zhou, personal name Ji Yijiu 姬宜臼 (also written 宜咎), was the first ruler of the Eastern Zhou dynasty 東周 (770-221 BCE). He was the oldest son of King You 周幽王 (r. 781-771).
Prince Yijiu was the son of Queen Shen 申后, and with the degradation of the Queen, Prince Yijiu also lost his father's favour and went into exile in his mother's homeland in Shen. His grandfather, Marquis Shen 申侯 took revenge and had the royal residence in Hao 鎬 attacked by the lord of Zeng 繒 and the Quanrong barbarians 犬戎. King You was killed, and Prince Yiji was proclaimed king in Shen.
With the support of the lords of Jin 晉, Zheng 鄭 and Qin 秦, he was escorted to Luoyang 洛陽, the secondary eastern capital, which was proclaimed main capital. The historical period beginning in this moment is therefore called the Eastern Zhou.
King Ping granted the regional ruler (zhuhou 諸侯) of Qin the title of duke. This was Duke Xiang 秦襄公 (r. 777-766), who was bestowed the ancient homeland of the Zhou around Qi 岐 and Feng 豐. The royal domain was reduced to a relatively small territory around the capital. The duke of Zheng and the king of Zhou exchanged their sons as hostages, in order to strengthen their political ties.