"Leading economists presenting fundamentally important issues in economic theory" is the theme of the Nancy Schwartz lectures series held annually at the J. L. Kellogg Graduate School of Management of Northwestern University. Reporting on lectures delivered in the years 1983 through 1997, this book discusses economic behavior at the individual and group level and the implications to the performance of economic systems. The lectures are delivered at a nontechnical level to benefit the newcomers, yet the overview of the distinguished lecturers is beneficial to seasoned researchers.