Alexander III was one of the most important popes of the Middle Ages and his papacy (1159-81) marked a significant watershed in the history of the Western Church and society. This book provides a long overdue reassessment of his papacy and his achievements, bringing together thirteen essays which review existing scholarship and present the latest research and new perspectives. Individual chapters cover topics such as Alexander's many contributions to the law of the Church, which had a major impact upon Western society, notably on marriage, his relations with Byzantium, and the extension of papal authority at the peripheries of the West, in Spain, Northern Europe and the Holy Land. But dominant are the major clashes between secular and spiritual authority: the confrontation between Henry II of England and Thomas Becket after which Alexander eventually secured the king's co-operation and the pope's eighteen-year conflict with the German emperor, Frederick I. Both the papacy and the Western Church emerged as stronger institutions from this struggle, largely owing to Alexander's leadership and resilience: he truly mastered the art of survival.
This series as a whole has a penchant for taking popes that are often underrated and demonstrating how important they actually were to the era in which they lived. Eugenius lived in the shadow of St. Bernard, Celestine was known as the old man who hung around for a while before Innocent III became pope, and Adrian is probably best known for the relatively trivial fact that he's the only pope from England. Though he's probably the most famous and well-respected of the lot, this work on Alexander continues the trend - Alexander is best known for his decades-long struggle against contemporary emperor Frederic Barbarossa, and it's easy to paint him as perpetually hounded by the forces that surrounded him. This work instead turns that into an asset for his pontificate, exploring how his frequent bouts of exile could function as a boon for the role of the papacy in general.
There are a lot of good essays in here - I particularly enjoyed one about the relationship between Alexander and the resurgent Roman commune written by John Doran - though some may be a bit dense or specific for someone without a good knowledge of what's going on with the papacy at this point (check out I.S. Robinson's The Papacy, 1073 1198: Continuity and Innovation for a work that's helpful for that).