This book is out of a workshop organized to address questions like these. The meeting was sponsored by the Santa Fe Institute and held at Sol y Sam- bra in Santa Fe, New Mexico, during July, 1993. It brought together a group of about 20 scientists from the disciplines of biology, psychology, and computer science, all studying interactions between the evolution of populations and individuals' adaptations in those populations, and all of whom make some use of computational tools in their work.