In view of the rapidly increasing complexity of conventional as well as hybrid powertrains, a systematic composition platform seeking for the global optimum powertrain is presented in this paper. The platform can be mainly divided into three parts: the synthesis of the transmission, the synthesis of the engine and the optimization and evaluation of the entire powertrain. In regard to the synthesis of transmission concepts, a systematical and computer-aided tool suitable both for conventional und hybrid transmission is developed. With this tool, all the potential transmission concepts, which can realize the desired driving modes or ratios, can be synthesized based on the vehicle data and requirements. As a result of the transmission synthesis, the detailed information of each transmission concept, including the transmission structure, the shifting logic, the estimated efficiency in each gear, and the estimated space arrangement of the transmission can be given out. The synthesis of transmission concepts is complemented by a comprehensive tool able to synthesize internal combustion engines of gasoline and gasoline/Atkinson type. The engine synthesis precalculates frictional and thermodynamic engine behavior and is validated by an ad hoc created database of over 200 engines, which serves as a comparison. Design parameters are deducted from this database in order to minimize the number of input parameters for the engine synthesis. The result of the engine synthesis is a map of the specific fuel consumption. The tool is implemented as a function to the overall powertrain synthesis and is triggered by an optimizer. Successively, the two synthesizing tools are joined in order to compose complete powertrain. Each powertrain concept consists of design parameters and corres-ponding configurations of synthesized engine and transmission. By varying these parameters, the different powertrains are further optimized and evaluated in consideration of the system efficiency and vehicle dynamics within the driving cycle. The whole optimization and evaluation process is repeated until the optimum powertrain is attained.