A decentralized, robust, multivariable controls method is described for the functional integration of subsystems in large-scale systems characterized by dynamic coupling among subsystem elements. In an integrated environment, a decentralized control structure reduces the complexity of the control by distributing the control authority to local controllers. The method relies upon generation of a set of control design specifications for the subsystems. The subsystem designers are provided with design specifications that provide for the integration of control functions. If the subsystem designers can satisfy these specifications, successful integration of the subsystem controls is guaranteed. The specifications are in terms of stability and performance robustness constraints in the frequency domain. The results are applied to an integrated flight-propulsion control example.