An invaluable resource to me lately has been The Oxford Companion to The History of Modern Science, edited by J.L. Heilbron(OUP, 2003). This is not a science encyclopedia but, as the title states, a companion guide to the history of science. The time covered is limited to the modern period, from around 1550, dwelling especially on seventeenth and eighteenth centuries, before closing with the development of modern scientific disciplines and their interactions with society in the beginning of the twenty-first century. Over 600 entries cover various scientific disciplines, historical developments in science, people, institutions, and other topics. It considers various approaches to the history of science including “feminist” and “Marxist”; includes entries on “Astrolabe,” “Astrophysics,” “Botanical garden,” “Hypothesis,” “Nazi science,” “Navigation,” “Oxygen,” and “Scientific Revolution.” The Companion is also playful, in that it includes entries on “Putti in Science,” “Slogans from Science,” and “Quark.” About 100 of the entries are biographical. There is a recommended reading list in the back, including guides to unpublished sources. There is even an index for “winners of the Nobel Science prizes,” from 1901-2002. Cross-references, a list of entries by broad topic, and an index facilitate ease of access. Authors of entries are identified after their articles and listed, along with their institutions. Entries are also accompanied by solid bibliographies. A directory of contributors (over 200) in the front of the book offers a “who’s who” of contemporary experts in various fields. Although hefty at 994 pages, it is one of the best single-volume treatments of its kind.