Cyber-Physical Systems (CPS) integrate embedded computers and networks with physical processes. They depend on feedback loops between computation and physical processes, data analytics, and AI. Their engineering needs unprecedented cooperation between different engineering disciplines. Development and deployment require new integrated scientific theories and engineering techniques. They will deliver advances in green buildings, autonomous vehicles, traffic flow management, emergency response, smart grids, industrial control, personalised healthcare, robotics, and other areas only now being envisaged. The journal Research Directions: CPS pushes the boundaries of research in the area to ensure smarter, more sophisticated solutions to intrinsically difficult research questions the community wants answered. Check out our most downloaded articles: