This work addresses the problems of simulating entire mixed analog/digital systems in the time-domain. A complete hierarchy of modelling and simulation methods for analog and digital circuits is described. It also provides a chronology of the research in the field of mixed-mode simulation and analog multilevel simulation over the last ten to 15 years. In addition, it provides enough information to the reader so that a prototype mixed-mode simulator could be developed using the algorithms in this book. The text can also be used as documentation for the SPLICE family of mixed-mode programs as they are based on the algorithms and techniques described in this book.