We describe compositional architectures and certifications in the research project certMILS. Compositional architectures enable re-use of certified COTS (commercial off-the-shelf) components with a well-defined delegation of responsibilities between component developers and system integrators during cyber physical system design and certification. We show how we used a Common Criteria certified MILS (Multiple Independent Levels of Safety / Security) platform for compositional designs and IEC 62443-4-1/62443-4-2 security evaluations and certifications for composed systems from the domains of smart grid, railway, and subway, that are safety-and security-critical.I.