The standard rationality hypothesis implies that behaviour can be represented as the maximization of a suitably restricted utility function. This hypothesis lies at the heart of a large body of recent work in economics, of course, but also in political science, ethics, and other major branches of social sciences. Though the utility maximization hypothesis is venerable, it remains an area of active research. Moreover, some fundamental conceptual problems remain unresolved, or at best have resolutions that are too recent to have achieved widespread understanding among social scientists. The main purpose of the Handbook of Utility Theory is to make recent developments in the area more accessible. The editors selected a number of specific topics, and invited contributions from researchers whose work had come to their attention. Therefore, the list of topics and contributions is largely the editors' responsibility. Each contributor's chapter has been refereed, and revised according to the referees' remarks. This is the first volume of a two volume set, with the second volume focusing on extensions of utility theory.