The main goal of model-based development is to produce high-quality soft- ware at acceptable cost. While high software quality can be achieved even now— as demonstrated by avionics software—, cost and development time are usually forbidding. Model-based development aims at improving not only the product, but also the process that leads to the product, making high-quality software development more affordable. In particular, it aims increasing the efficiency of the development not only of single products but of related product families.