Artificial life is a new field of scientific inquiry that studies biology by attempting to synthesize such biological phenomena as life, evolution, and ecological dynamics within computers and other "artificial" media. In addition to uncovering new ways to study life as we know it, a life extends research to the larger domain of life as it could be, whatever it might be made of and wherever it might be found in the universe.This proceedings volume, based on the second artificial life workshop held in Santa Fe, New Mexico, 1990, reflects the evolution and horizons of this rich field of study, and builds on the proceedings of the seminal first workshop, held at Los Alamos in 1987 (also available from Addison Wesley). This compendium includes more than 30 papers spanning the spectrum of a-life research, from studies of the origin of life to models of complex systems.