MARS , which stands for Multi Access seat Reservation System, is a train ticket reservation system used by the Japan Railways Group companies and travel agencies in Japan. It was developed jointly by Hitachi and the former Japanese National Railways (JNR), and inherited by the Railway Information Systems Company, which is jointly owned by the seven railway companies of the JR Group: the East Japan Railway Company, Central Japan Railway Company, West Japan Railway Company, Hokkaido Railway Company, Shikoku Railway Company, Kyushu Railway Company, and Japan Freight Railway Company.

Computer reservation systems, or central reservation systems (CRS), are computerized systems used to store and retrieve information and conduct transactions related to air travel, hotels, car rental, or other activities. Originally designed and operated by airlines, CRSs were later extended for use by travel agencies, and global distribution systems (GDSs) to book and sell tickets for multiple airlines. Most airlines have outsourced their CRSs to GDS companies, which also enable consumer access through Internet gateways.