Over the last twenty to thirty years the progressivcly increasing availability of averaging machines has made evoked potential testing available not only in the major neurological diagnostic centers but also in the office of many neuro logists in private practice. This rapid devclopment was closely paralleled by clinical research in evoked potentials and the publishing of books covering in detail the basic techniques necessary to obtain evoked potentials and the main clinical applications of evoked potentials. Less work was done, however, to define some of the general principles underlying the recording of evoked potentials or to analyze critically the recording techniques or the actual prac tical value of the information provided by evoked potential testing. In this book an attempt has been made to cover this gap. It is assumed that the reader has a good understanding of basic recording techniques and is familiar with the main applications of clinical evoked potentials. The main emphasis of the first two chapters is to define with more precision some of the physical principles that inftuence the volta ge distribution and are used for defining the generator sources of evoked potentials. This is followed by a critical analysis of recording techniques and of its main clinical applications. Finally there is one chapter that gives an overview on application of evoked potentials for surgical monitoring. This is a rapidly growing field that also has been covered only incomplctcly in previous publications.