The problem of tracking time-varying trajectories in non-linear systems is considered. These trajectories could be generated on-line by a reference model. The problem is tackled by considering the overall system as a set of decentralized linear sub-systems which can be modelled as a set of double integrators and treating the non-linearities as uncertainties with known bounds on their magnitudes. A variable structure controller is designed based on the theory of uncertain dynamical systems. The system is shown to track a class of trajectories generated by the reference mode! (a set of double integrators) to within a specified tolerance. Some analysis is presented to explain the dynamic behaviour of the closed-loop system and bounds are derived linking the rate of convergence and the tracking ability to system parameters such as available control and magnitude of the uncertainty. Simulation results are presented to validate the conclusions.