This chapter discusses optimal control techniques for industrial control system design problems. The author divides such problems into four categories: 1) Simple loops well-solved by PID control, 2) Slightly more complex problems helped by tools like feedforward or Smith prediction, 3) Systems with interactions addressed by preliminary compensation, and 4) Difficult problems requiring computer-assisted optimization, which is the focus of this chapter. The chapter presents methods for solving category 4 problems using optimal control theory and the linear quadratic regulator (LQR) approach. It derives the necessary conditions and continuous-time dynamic Riccati equation for optimal control and discusses properties of the LQR solution like stability and convergence.