This talk reports on some of the results obtained in the ProCoS project. The main emphasis will be on methods for the early phases in the development of a system: requirements capture and high\discretionary-level system design. 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.