The dual goals of low emissions and improved fuel economy have raised concern over the spark ignition engine's ultimate capability to meet our country's long-term social needs. This has heightened the interest in alternate powerplants for passenger cars. There are eight types of powerplants that merit serious consideration in the next twelve years that will be discussed. Each of the candidates represent a unique set of trade-offs and risk. The candidates will be arranged in the following categories: current or near-term technology, advanced heat engine technology, and new technology. Engineering, legal, economic, and social factors will be discussed for each category.