The 921 earthquake (Chinese: 九二一大地震; pinyin: Jiǔ'èryī dàdìzhèn), also known as Jiji earthquake (Chinese: 集集大地震; pinyin: Jíjí dàdìzhèn), was a 7.3 M_s or 7.6 M_w earthquake which occurred at 1:47:12 am local time on Tuesday, September 21, 1999 (17:47:12 UTC on September 20) in Jiji (Chichi, 集集), Nantou County, Taiwan. 2,415 people were killed, 11,305 injured, and NT$300 billion (US$10 billion) worth of damage was done. It was the second-deadliest quake in recorded history in Taiwan, after the 1935 Hsinchu-Taichung earthquake.

Rescue groups from around the world joined local relief workers and the ROC military in digging out survivors, clearing rubble, restoring essential services and distributing food and other aid to the more than 100,000 people made homeless by the quake. The disaster, dubbed the "Quake of the Century" by local media, had a profound effect on the economy of the island and the consciousness of the people, and dissatisfaction with government's performance in reacting to it was said by some commentators^[who?] to be a factor in the unseating of the ruling Kuomintang party in the 2000 Presidential Election.