Designed for use by professional researchers and advanced graduate students, this text forms part of a series of handbooks for various branches of economics, each of which is a source, reference and teaching supplement. Each handbook provides self-contained surveys of the current state of a branch of economics in the form of chapters prepared by leading specialists on various aspects of this branch of economics. These surveys summarize not only received results but also newer developments from recent journal articles and discussion papers. Some original material is also included.