Unfalsified control theory is a variant of adaptive control techniques. The main attractive point of this approach is that no plant model is required to design an adaptive controller. Following this concept, an adaptive controller is implemented by means of switchings among many candidate controllers in a predefined set. The plant input signal and the plant output signal are observed while one candidate controller is active in the feedback loop, and they are used for the unfalsification procedure to decide on which candidate controller in the set should be switched on as the next active controller. In the original work of Safonov et al., the adaptation of controllers can only be performed using the switching of an active controller in a predefined set of controllers. This is a major limitation to apply this approach to a nonlinear system. Usually, a fixed set of controllers that performs well for one operating point cannot guarantee to achieve a good performance under other operating conditions.To solve the above problem, when a new operating condition occurs, a new set of controllers is computed using a new cost function developed in this thesis and an evolutionary algorithm is used in order to search for an optimal controller over aspace of arbitrary candidate controllers. A combination of the switching of controllers in the current set and the adaptation of the set of controllers leads to an automatie controller tuning method for a controller structure, e.g. PI and PID, in order to handle changes of set-points occurring in a highly nonlinear chemical process, e.g. a continuous stirred tank reactor (CSTR). Such a combination as proposed in this thesis is the so-called a new unfalsified adaptive control algorithm.A necessary condition of adaptive control systems is closed-loop stability or that adaptive control algorithm must be safe. Otherwise, in practice, it cannot be used. Since the proposed algorithm is meant to apply for a nonlinear stable plant, we prove that it can guarantee stability if there is at least one stabilizing controller in the current set of candidate controllers. The switching of the controllers eventually stops and the final active controller in the current set is a stabilizing controller.