The control systems considered in the preceding chapters are SISO systems. In these systems, the plant has only a single output and a single manipulated input. Some systems are MIMO systems, in which the plant has more than one output and requires more than one manipulated input. From this chapter on, the analysis and design of MIMO systems will be the main subject. The discussion will concentrate on the square plant, that is, the plant with the same number of inputs and outputs.