I absolutely love these books. There is so much information, covering such a range of people and time periods. As a History of Science student, I use these volumes for every single essay I write. Some of the more famous scientists have entries that are pages and pages long, while some of the more obscure entries are only a few paragraphs. There is SO much information in the volumes that I can't imagine looking anywhere else for references. Later this year, a new edition will be published, which will include scientists from the last few decades and new historical figures not included in past editions.