A History of the Inquisition of the Middle Ages in three volumes is a groundbreaking work on the subject of Inquisition, written by Henry Charles Lea, one of the main authorities on the subject. His goal was to present an impartial account of the institution as it existed during the earlier period. In order to accurately appreciate the process of its development and the results of its activity the author takes in consideration the factors controlling the minds and souls of men during these times. He recapitulates nearly all the spiritual and intellectual movements of the Middle Ages, glancing at the condition of society in certain of its phases. Beginning with the state of church in 12th and 13th century, the study includes various forms of heresy emerging throughout the European continent from Spain and France west, to Slavic countries in Eastern Europe. Lea particularly deals with various fields of inquisitorial activity, notably its utilization in political purposes. Though his study of the Inquisition was criticized for anti-Spanish bias, it is thoroughly researched and contains interesting details surrounding this notorious institution.

Henry Charles Lea (1825-1909) was an American historian, civic reformer, and political activist. Lea focused on history, mainly on church history in the later Middle Ages, and on institutional, legal, and ecclesiastical history, as well as magic and witchcraft. During the American Civil War Lea was a member of the Union League of Philadelphia and headed its publication committee, writing many of the League's published pamphlets.