This article summarizes Walter Isard’s important contributions to environmental economics and ecological economics. The former is the traditional field that incorporates some limited aspects of the environment into neoclassical economic theory, while the latter is a more comprehensive integration of economic and ecological principles in a set of eclectic frameworks. Walter’s contributions include pioneering research, primarily in a spatial context, and the mentoring of prominent researchers in these fields during the period of 1965–75. We examine these contributions in the context of the state of the art of knowledge in these fields at the time and today. We also discuss Walter’s influence in Europe in these areas. We conclude with a discussion of some promising new directions, with an emphasis on regional science dimensions.