Book excerpt: The aim of each volume of this series Guides to Information Sources is to reduce the time which needs to be spent on patient searching and to recommend the best starting point and sources most likely to yield the desired information. The criteria for selection provide a way into a subject to those new to the field and assists in identifying major new or possibly unexplored sources to those who already have some acquaintance with it. The series attempts to achieve evaluation through a careful selection of sources and through the comments provided on those sources.