This book presents both continuous-time and discrete-time systems, and brings out the similarities which reinforce many ideas. Also, an attempt has been made to point out many exceptions that occur which warrant a careful study in each case. Special attention has been given to important control problems such as deadbeat control, non-zero set points, and external disturbances and sensitivity problems in optimal linear regulators. The recent proposals for system design have been emphasized, such as modal control, state observers and estimators, suboptimal control, etc.