Mount Bailey is a relatively young tephra cone and shield volcano in the Cascade Range located opposite Mount Thielsen from Diamond Lake in southern Oregon, United States. Bailey consists of a high main cone on top of an old basaltic andesite shield volcano. With a volume of , Mount Bailey is slightly smaller than its neighbor Diamond Peak.
Mount Bailey has become well known in the Pacific Northwest region as a haven for "snowcat skiing" in the winter months. Instead of a conventional chairlift, snowcats—treaded, tractor-like vehicles that can ascend Bailey's steep, snow-covered slopes—carry skiers to the higher reaches of the mountain. In the summer months, a hiking trail gives foot access to Bailey's summit.
Native Americans are credited with the first ascents of Bailey. It was considered a sacred place to them and a source of medicine (healing) where spiritual leaders would hold feasts and prayer vigils on the summit.
The origin of the mountain's name is a matter of dispute. Old maps show its name as either "Old Baldy" or "Old Bailey", with "Bailey" possibly being a drafting error, while the summit's bald, burnt-over appearance might indicate the origin of the designation "Baldy". No record of a person named Bailey who was connected with the peak has been found.
The Klamath name for the mountain was Youxlokes, which means "Medicine Mountain".