Milestones in Current Research is a series of reprint collections dis­ tinguished from other such publications by new concepts in preparation, presentation, and intent. The aim of each volume is to gather for a given field the seminal contributions that have defined and shaped the trends within the most active areas of current research. The selections for each volume and the structure of the book have been determined with the help of a novel tech­ nique of bibliographic analysis and have then been presented to an acknowl­ edged scientific authority for minor adjustments and the writing of an In­ troduction. These introductions will lend historic perspective to the material selected for each volume. The bibliographic analysis used tends to select papers central to the areas of current research within, roughly, the last decade and is a systematic procedure for depicting, delineating, and covering all such areas over a wide spectrum of scientific research. It is hoped that with this procedure it will be possible to achieve an objectivity, authority, and thoroughness not reached by others and that the timeliness of the volumes will not be limited to just a few years. Each volume should have the permanent value of a historical statement and yet be suf­ ficiently interesting to active researchers in the field as well as to students exploring the quiet way in which the relentless drama of research unfolds in the journal literature.