The Encyclopedia of Ephemera is the fruit of Maurice Rickards' lifetime's work in establishing a collection which would illustrate all types or genres of ephemera. He sadly died (in 1998) before finishing the encyclopedia and the work was completed and edited by Prof Michael Twyman, aided by Sally du Boscq de Beaumont and Amoret Tanner, all of the Centre for Ephemera Studies in the Dept of Typography, University of Reading, where the Rickards Collection is now housed. It was published in 2000 by the British Library.
Copiously illustrated and with substantial entries on each category of ephemera from ABC primer to zoetrope strip/disc, the encyclopedia is an essential reference work for anyone interested in ephemera per se or in subjects represented by ephemera. There are two editions, one British, one American. Although there is not officially an electronic version of the encyclopedia, substantial snippet views appear through Google books.
The work of defining categories and genres of ephemera continues at the Centre for Ephemera Studies where a thesaurus of genre terms for ephemera is in preparation.