In this chapter, we start our examination of the development of decentralized control techniques for interconnected systems where we focus on the classes of nonlinear continuous-time systems. We focus on interconnected minimum-phase nonlinear systems with parameter uncertainty and bounded and/or strong nonlinear interconnections. The objective is to design a robust decentralized controller such that the closed-loop large-scale interconnected nonlinear system is globally asymptotically stable for all admissible uncertain parameters and interconnections. The design is recursive in nature. By employing performance, the solution of the decentralized control problem is attained via the Hamilton-Jacobi-Isaacs (HJI) inequalities. Finally, a decentralized output-feedback tracking problem with disturbance attenuation is addressed for a new class of large-scale and minimum-phase nonlinear systems. Application of decentralized stabilization and excitation controls of multimachine power systems are demonstrated.