With an aim at providing more people with the fun in motorcycling, Honda has been developing various types of automatic transmissions. The hurdles are especially high for an automatic transmission for large motorcycles to satisfy a variety of requirements under various conditions such as when engine braking, when in partially-opened throttle, etc. along with the needs of durability, efficiency, and compactness. Through the R&D efforts over a long period of time, Honda has developed the hydraulic mechanical transmission called HMT, which efficiently uses the power transmission capabilities of both hydraulic and mechanical systems, as the technology that opens up a new possibility of an automatic transmission. Honda started the development of HMT in the 1950’s and applied it to motocross machines in order to polish the system through the real-world of motorcycle racing. In the year 2000, the electronic control system was added, and thus developed a strong and easy-to-use, high-performance automatic transmission named “Hondamatic”, which was applied it to the ATV (all terrain vehicle). Explained hereafter is the development history of the unique HMT and its mechanism.