Amazon.com (ISBN 0195221869, Paperback)

Although not for every opera lover (or every opera lover's budget), this massive four-volume set--each volume coming in at around 1,300 pages--is indispensable for the opera educator, writer, or major fanatic. While in any encyclopedia the quality of writing and the critical viewpoint must of necessity be somewhat varied, the standards in the Grove series of reference works are always high and the level of usefulness enormous. Almost any opera that debuted before 1992 is to be found within these pages, making it especially useful in this age of obscure revivals; most singers of any note who had established careers before that date are also included. Although somewhat Anglocentric in its inclusions, this remains an invaluable reference work.