The present work is concerned with the design of PID controllers, calculation of set point weighting parameter and identification of transfer function models for unstable systems with time delay and without or with a zero. Synthesis method, IMC method and Equating coefficient method are proposed for design of PID controllers. Three methods are proposed to calculate the set point weighting parameters. Closed loop reaction curve method and optimization method are proposed for identifying transfer function models. Several simulation examples on transfer function models of FCC reactor, distillation column, crystallizer, exothermic CSTR and nonlinear models of CSTR, Co-Polymerization reactor are given to show the effectiveness of the proposed methods. Since steady-state multiplicity arises in chemical systems, biological systesm, separation processes, fluid mechnical systems and recycle processes, the methods proposed in this monograph will be useful to design controllers for such systems.