An onsen (温泉^?) is a term for hot springs in the Japanese language, though the term is often used to describe the bathing facilities and inns around the hot springs. As a volcanically active country, Japan has thousands of onsen scattered along its length and breadth. Onsen were traditionally used as public bathing places and today play a central role in directing Japanese domestic tourism.

Onsen come in many types and shapes, including outdoor (露天風呂 or 野天風呂, roten-buro or noten-buro^?) and indoor baths. Baths may be either public run by a municipality or private (内湯, uchiyu^?) often run as part of a hotel, ryokan or bed and breakfast (民宿, minshuku^?).

Onsen are a central feature of Japanese tourism often found out in the countryside but there are a number of popular establishments still found within major cities. They are a major tourist attraction drawing Japanese couples, families or company groups who want to get away from the hectic life of the city to relax. Japanese often talk of the virtues of "naked communion" (裸の付き合い, hadaka no tsukiai^?) for breaking down barriers and getting to know people in the relaxed homey atmosphere of a ryokan with an attached onsen. Japanese television channels often feature special programs about local onsens.