This volume is the result of a symposium entitled Variation in Life Histories: Genetics and Evolutionary Processes sponsored by the Program in Evolutionary Ecology and Behavior of the University of Iowa and held in Iowa City on October 13 and 14, 1980. Prompted by a recent upsurge of interest in the evolution of life histories, we chose this topic because of the obvious association between life history traits and Darwinian fit ness. If such an association were to be fruitfully investigated, it would require the closer cooperation of population and evolutionary ecologists and quantitative and population geneticists. To encourage such an association, our symposium had four major aims: first, to facilitate intellectual exchange across disciplines among an array of biologists studying life histories; second, to encourage exploration of genetic variance and covari ance for life history traits; third, to consider the ecological background for genetic vari ability; and finally, to facilitate a comparative overview both within and among species. Obviously such broad aims cannot be met totally in a single volume, but we think we have succeeded reasonably well in providing a representative and nourishing intel lectual feast. We see this book as a stimulus to the coordination of future efforts in an important and expanding area of inquiry. We have divided the book into six sections.