This monograph is devoted to a rigorous presentation of results about the representation of preference orderings by real-valued order isomorphisms ("utility functions"). The authors have gathered together, from sources scattered throughout a wide range of the literature of mathematics and economics, the most significant theorems and methods in their field. The book will be a valuable resource for theoretical economists, mathematicians, and all interested in partial orders and their representation. It could also be used as the text for an advanced graduate course in mathematical economics.