Pope from 1216. Succeeding Innocent III, he was involved in implementing his predecessor's policy and the decrees of the Fourth Lateran Council. He crowned the Emp. Frederick II in 1220 and took a prominent part in the political affairs of Europe. He approved the Dominican, Franciscan, and Carmelite Orders and fostered the growth of their Third Orders. He was the author of the Liber Censuum (q.v.).