The problem of the decentralized control of a linear interconnected dynamical system is considered. This is done by defining the problems of the decentralized controllability and of the decentralized observability, which are solved for a system consisting of two interconnected scalar systems. The solution is determined using the theory of the linear dynamical systems in the differential operator representation (Wolovich 1974), and provides, besides structural results, a systematic method for the decentralized control of these systems.