Sir Hugh Munro published his first list of Scottish mountains above 3000 feet back in 1891. These mountains have since become known as Munros, and today consists of 284 mountains. The last revision to the list was made in 1997.
The only real criteria for being on the list is that the mountain is located in Scotland, and that it has a height of at least 3000 feet (~914 metres); there is no definite requirements in terms of primary factor.