Over the last decade the field of adaptive control where no identification mechanisms are invoked has become a major research topic. This book presents a state-of-the-art report on the following more specific area: the system classes under consideration contain linear (possibly nonlinearly perturbed), finite dimensional, continuous time systems which are stabilizable by high-gain output feedback. The properties of minimum phase systems and strictly positive real systems are studied in their own right. These results are applied to design simple adaptive controllers involving a switching strategy which is mainly tuned by a one parameter controller based on output data alone. Control objectives are stabilization, tracking, -tracking and servomechanism action. In addition, robustness with respect to nonlinear perturbations and performance improvements are investigated.