Qaen (Persian: قائن)[a] is a city in the Central District of Qaen County, South Khorasan province, Iran, and serves as capital of both the county and the district.

[4] One of the first Paleolithic signs was discovered in a village called Khonik in the city of Qain.

(qayen or Ghayen)[5] The Middle Persian work Shahrestaniha i Eranshahr mentions this city, and attributes its foundation to Sined Ninoh Kitop in 1588.

[6] At the time of the 2006 National Census, the city's population was 32,474 in 8,492 households.

[8] The 2016 census measured the population of the city as 42,323 people in 11,920 households.