This paper outlines the usage and background of hot springs in Japan, known as “ONSEN” in Japanese, focusing on the regulatory science approach, and summarizes the definition and development systems of hot springs based on the Hot Springs Law. In accordance with this law, all prefectures receive an annual report on usage status from hot spring companies, which is converted into data by Japan’s Ministry of the Environment. According to the data, hot spring development peaked around FY2006–2007. Since then, the total number of hot springs has leveled off, albeit with a decreasing trend first, and currently a stable trend. In addition, the regional characteristics of volcanic regions such as the Kyushu and Okinawa regions, and non-volcanic regions such as the Kinki, Chugoku, and Shikoku regions, are reflected in the temperatures of the springs and artesian hot spring rates. Unlike other countries where geochemical samples are usually extremely difficult to obtain, Japan’s unique environment makes geochemical samples easily and continuously available. Therefore, Japan can be considered to be an extremely attractive research field for geochemists. However, it is necessary to exercise caution, because the development of hot springs involves not only geological and geochemical natural conditions, but also factors, such as economic conditions and population density.