The understanding of parallel processing and of the mechanisms underlying neural networks in the brain is certainly one of the most challenging problems of contemporary science. During the last decades significant progress has been made by the combination of different techniques, which have elucidated properties at a cellular and molecular level. However, in order to make significant progress in this field, it is necessary to gather more direct experimental data on the parallel processing occurring in the nervous system. Indeed the nervous system overcomes the limitations of its elementary components by employing a massive degree of parallelism, through the extremely rich set of synaptic interconnections between neurons. This book gathers a selection of the contributions presented during the NATO ASI School "Neuronal Circuits and Networks" held at the Ettore Majorana Center in Erice, Sicily, from June 15 to 27, 1997. The purpose of the School was to present an overview of recent results on single cell properties, the dynamics of neuronal networks and modelling of the nervous system. The School and the present book propose an interdisciplinary approach of experimental and theoretical aspects of brain functions combining different techniques and methodologies.