The development of a control systems theory for multidimensional linear systems, i.e. systems with more than one independent variable is an area where a very significant volume of research is based on representations for the underlying dynamics introduced in the 1970s. One of these is the Fornasini-Marchesini state-space model published in 1978. This paper reviews the significant developments in the succeeding four decades in both theory and applications, including examples where this model description is an enabler for the analysis of other classes of systems.