ProCoS is an EU-funded research project with the overall goal to advance the state of art of systematic design of complex heterogenous systems, and in particular to reduce the risk of error in the specification, design and implementation of embedded safety-critical systems. The ProCoS methodology uses a formal notation where correctness of a design relative to a set of requirements can be verified by mathematical reasoning. The notation comprises a real-time logic, the Duration Calculus, which is used in expressing real-time properties of systems and components.