This book concerns the relations between Honorius III (1216–1227) and the Emperor Frederick II (1220–1250) and argues for the importance of Honorius III in the promotion of two crusades, the Fifth Crusade (1218–1221) and the Imperial Crusade (1221–1227), and, more broadly, that Honorius deserves to be considered seriously as a pope who was at least as effective as his illustrious predecessor, Innocent III (1198–1216), and successor, Gregory IX (1227–1241). The work further argues for the reactive nature of papal government and the danger of thinking in terms of the papacy developing policies. The study is based in the main on papal letters, particularly those in the papal registers. The work is divided into three parts, with the first part being concentrated on a description of the papal chancery and the construction of the letters. The second part is an account of papal dealings with King Andrew II of Hungary (1205–1235), arguing that he was the initial leader of the crusade, followed by the pope's negotiations with Frederick II. The third part is concerned with the means of enhancing papal authority through the arengae (preambles) of the papal letters, the use of legates, and taxation. Honorius, as Cardinal Cencius (not of the Savelli family) is presented as a self-made man—self-described as raised by and through the Roman Church from infancy—rather than a man of the schools like Lothar of Segni (Innocent III). Experienced as compiler of the Liber Censuum (the papal accounts of what it was owed in each region by churches and secular rulers), chancellor, and chamberlain, Honorius is presented as dealing with the recalcitrant Frederick patiently and usefully, since the emperor would set out to Jerusalem and ultimately negotiate its return to Christian hands.

The work does suffer from some problems of structure, which make it more difficult to sustain the argument. Historians of the papacy are likely to be frustrated by the initial one hundred pages, which concentrate on a description of the chancery and papal diplomatic, all of which will be familiar to them. That may go at times for the section on the arengae as well, while the final section on taxation should surely have more prominence because it was here that Honorius III brought his lifetime of expertise to bear and showed himself superior to Innocent III, whose failure to finance the Fourth Crusade properly had lasting consequences.

Honorius III has undoubtedly not received the attention of Innocent III, but Innocent is considered one of the most capable and influential men ever to become pope. It was Innocent III who called and organized the Fourth Lateran Council of 1215, which was the major ecclesiastical council of the Middle Ages. It was Innocent who recognized that Francis of Assisi might rescue the ailing church. It was Innocent who came to be considered one of the supreme lawgivers in the history of humankind. Moreover, in politics, Honorius tended to opt for conciliation and compromise while Innocent chose to bring his opponents to heel in his devotion to his bride, the ecclesia romana. There were good reasons, then, why the cardinals in 1198 opted for Lothar and not Cencius, even though Cencius was the more experienced of the two. But they and the cardinals subsequently chosen by Innocent III opted for Cencius eighteen years later, suggesting that the antipathy between the two men was not as great as is sometimes suspected. Although the author initially argues for a papacy that is not generally proactive, across the book a rather different picture emerges. Papal government, like most government most of the time, did react to the problems brought to it and often tried, where it could, to accommodate those who sought its aid. Yet the arengae, even though one cannot confidently attribute more than a few of them to the mind of the pope himself, show the papacy aiming actively to influence the thought of its multiple audiences, ecclesiastical and lay, with ideologies that have some coherence. As the author points out, each legation is different, but the pope did oversee his legates, particularly the much maligned Cardinal Pelagius, who followed his master's instructions to a surprising degree. And even though there were inconsistencies in papal action, as when money that could have been used for the crusade to the Holy Land was redirected to the Albigensian crusade or to Spain, nevertheless, the collection and distribution of the tax of the twentieth was the result of papal initiative.

This work is a valuable addition to the literature on the papacy of the thirteenth century and helps us to understand the relationship between the papacy and the empire in those moments before the conflict between Frederick and Gregory IX, which would have lasting implications for the West. It was not the fault of Honorius III that the impressive support he gave to Frederick II would result in a crusade that would not only recover Jerusalem but also see it lost for good.