The causes of the explosion are not easily identifiable, although it is clear that one of the factors which has propelled it is the need felt by academic institutions (and, regrettably, governments) to measure individual scholarly performance, and the concomitant expectation that a young scholar will publish one book (or more) to achieve tenure, a second book to secure further promotion, and a substantial number of books and articles to attain to the highest academic posts. Given these circumstances, it is not surprising that the past few decades have seen the creation of various sorts of bibliographies and encyclopedias designed to provide streamlined guidance to the essential scholarship on a given medieval topic. We are unaware of a comparable work of reference on the Middle Ages which offers so much detailed information at a price which individual medievalists will be able to afford.