This paper presents a general framework for disturbance observer based control (DOBC) for nonlinear systems. The approach, called nonlinear DOBC (NDOBC), divides the control problem into two subproblems: one for stabilizing the system and achieving performance specifications, and another for attenuating disturbances. A nonlinear disturbance observer is designed to estimate external disturbances and compensate for their effects. The method is illustrated by the application to control of a two-link robotic manipulator. The paper introduces a two-stage design procedure for DOBC. In the first stage, a controller is designed assuming no disturbances or measurable disturbances. In the second stage, a nonlinear disturbance observer is designed and integrated with the controller to enhance disturbance attenuation. The nonlinear disturbance observer is designed to estimate disturbances generated by an exogenous system, and global exponential stability is established under certain conditions. A semiglobal stability condition for the composite controller is also established. The paper develops a nonlinear disturbance observer for disturbances generated by a linear exogenous system. The design of the observer is based on the algebraic structure of the nonlinear system. The observer is shown to be globally exponentially stable under certain conditions. The paper also establishes semiglobal exponential stability for the composite controller consisting of a nonlinear controller and the nonlinear disturbance observer. The paper demonstrates the effectiveness of the NDOBC approach by applying it to the control of a two-link robotic manipulator. The results show that the NDOBC significantly improves disturbance attenuation ability compared to traditional control methods. The paper concludes that the NDOBC approach is flexible and can be integrated with existing linear and nonlinear control methods to enhance disturbance attenuation. Theoretical results are provided, including global exponential stability of the nonlinear disturbance observer and semiglobal exponential stability of the composite controller.This paper presents a general framework for disturbance observer based control (DOBC) for nonlinear systems. The approach, called nonlinear DOBC (NDOBC), divides the control problem into two subproblems: one for stabilizing the system and achieving performance specifications, and another for attenuating disturbances. A nonlinear disturbance observer is designed to estimate external disturbances and compensate for their effects. The method is illustrated by the application to control of a two-link robotic manipulator. The paper introduces a two-stage design procedure for DOBC. In the first stage, a controller is designed assuming no disturbances or measurable disturbances. In the second stage, a nonlinear disturbance observer is designed and integrated with the controller to enhance disturbance attenuation. The nonlinear disturbance observer is designed to estimate disturbances generated by an exogenous system, and global exponential stability is established under certain conditions. A semiglobal stability condition for the composite controller is also established. The paper develops a nonlinear disturbance observer for disturbances generated by a linear exogenous system. The design of the observer is based on the algebraic structure of the nonlinear system. The observer is shown to be globally exponentially stable under certain conditions. The paper also establishes semiglobal exponential stability for the composite controller consisting of a nonlinear controller and the nonlinear disturbance observer. The paper demonstrates the effectiveness of the NDOBC approach by applying it to the control of a two-link robotic manipulator. The results show that the NDOBC significantly improves disturbance attenuation ability compared to traditional control methods. The paper concludes that the NDOBC approach is flexible and can be integrated with existing linear and nonlinear control methods to enhance disturbance attenuation. Theoretical results are provided, including global exponential stability of the nonlinear disturbance observer and semiglobal exponential stability of the composite controller.