Concise Encyclopedia of the Bahai Faith. Main BP 327 .C66 2000
Historical Dictionary of the Bahai Faith. Main BP 327 .A33 1998
Basic Bahai Dictionary. Main BP 365 .B3 1989
The second is a Scarecrow Press publication, in dictionary arrangement with biographical and topical entries from a paragraph to a couple of pages long. The third is published by George Ronald, a primary publisher of Bahai materials, in England. It is arranged similarly but also has black and white illustrations.