This volume contains the proceedings of the DIMACS Workshop on Expander Graphs, held at Princeton University in May 1992. The subject of expanding graphs involves a number of different fields and gives rise to important connections among them. Many of these fields were represented at the workshop, including theoretical computer science, combinatorics, probability theory, representation theory, number theory, and differential geometry. With twenty-two talks and two open problem sessions, the workshop provided a unique opportunity for cross-fertilization of various areas. This volume will prove useful to mathematicians and computer scientists interested in current results in this area of research.