The control volume approach, if appropriately applied, can yield information on the dependencies among various variables on compressible flow systems, which is very useful for parametric studies. The complex internal compressible flows presented here fall into the following categories: steady flows through variable area ducts with and without heat addition and friction, nozzle starting and choking, shock trains, shock tubes, and unsteady flows inside angled‐bend ducts. Ram/Scram jet engines and ejectors are described, as they are representative examples of complex flow systems.