In the fall of 1990 I had just began my doc- toral studies at the University of Connecticut. Freshly arrived from Italy, I came to the United States to work with Carl Schlichting on something to do with phenotypic plastic- ity. I spent most of that semester discussing with other graduate students what I thought was a momentous paper by Mary Jane West- Eberhard (1989) in the Annual Review of Ecol- ogy and Systematics. That paper, entitled Phe- notypic Plasticity and the Origins of Diversity, was a (quite lengthy) forerunner of the (also quite bulky) book I am reviewing now. Like the paper, this volume has the potential to be momentous in the development of our ideas on phenotypic evolution.