1. An adaptive controller for use in controlling a process, comprising: a controller input to receive an process variable input signal from the process; a controller output to provide a process control signal for use in controlling the process; a control block coupled between the controller input and the controller output that determines the control signal by implementing process control calculations using the input signal and a set of controller tuning parameters; and a tuning block that determines new values for the set of controller tuning parameters during operation of the process using a set of stored process model parameter values and a process state variable, wherein the set of stored process model parameter values includes a process model parameter value for a particular process model parameter for each of a plurality of different process operating points defined by the process state variable; the tuning block including; a model adaptation routine that determines the stored process model parameter value for the process model parameter at each of the plurality of different process operating points; a model parameter determination routine that determines a particular process model parameter value for a particular process operating point based on the process state variable value and the set of stored process model parameter values; and a controller tuning parameter routine that determines the set of controller tuning parameters for the particular process operating point from the determined process model parameter value and a stored tuning rule.