The concept and characteristics of the propulsion systems for the next generation flight vehicles are described in this paper, where Hey are grouped into air breathing engine, rocket engine and combined cycle engine according to the feeding system of oxidizer. Air breathing engine has its good reusability and superior performance at low altitude, but its usage is limited at high altitude due to the decreased air density. Rocket engine can be used over the wide range of altitude, but it has disadvantages in low specific impulse and high cost. The several types of combined cycle engine, which are being developed by the leading countries in the aerospace, are highlighted as a remarkable candidate for the next generation propulsion system.