This work deals with the tracking control of nonlinear mechatronic systems with unknown parameters. In the first part of the book an extended robust-adaptive control law and a supervisory control law is proposed for nonlinear mechatronic systems to achieve increased robustness in the presence of large modelling uncertainties. The proposed control laws are applicable to under-actuated mechatronic systems. The second part of the book deals with the friction in mechatronic systems. A general friction model is proposed that describes well the nonlinear behavior of friction and at the same time it can easily be introduced in adaptive control algorithms. A parameter identification method for the developed model is introduced. Based on the model a friction compensation algorithm is developed that guarantees high tracking accuracy in the presence of dominant frictional effects. Finally, an adaptive tracking control algorithm is proposed for robotic systems to solve simultaneously the friction compensation and payload estimation problem. The developed control law can guarantee prescribed tracking accuracy in the presence of unknown friction parameters and payload mass.