The linear quadratic regulator can generate an offset if either the unmeasured disturbances are non-stationary, i.e. they have slowly drifting behaviour, or there is a mismatch between the plant and the model. As a remedy one can introduce an integral action in the control to deal with plant-model mismatch and reject the drifting unmeasured disturbances. Observe that the regulator solves the problem of moving the system from any initial state to the origin. If it is desired to move the system from any initial condition to an arbitrary set-point, the state feedback control law has to be modified. The problem of regulation in the presence of unknown disturbances, plant-model mismatch and tracking an arbitrary set-point trajectory is solved by modifying the regulatory control law as uk-us=-K(xk-xs), i.e., uk=us-K(xk-xs), where xs represent the steady state target corresponding to the set-point, say r, and us represents the steady state input necessary to reach this steady state target. This is equivalent to the change of the origin. In this section, we discuss various approaches to incorporate regulation in the presence of drifting disturbances and tracking arbitrary set-point changes.