In recent years study of the First Crusade has focused on its devotional characteristics and military encounters, and the expedition's social profile has been neglected. This book is an attempt to fill that gap, and it is welcome because, as its author states in his final paragraph, ‘approaching the subject with an interest in social dynamics unlocks a great deal of unappreciated content in the source material’. The wealth and variety of contemporary narrative about the crusade hold the potential to act as a window into the society that created the armies, while close analysis of the social origins and collective identities of those who took the cross ought to assist us in assessing their motivations. That said, the task brings with it enormous problems and they are all too evident in Kostick's monograph. The crusade took place at a time of rapid social change, which was reflected throughout the language that its historians used. Key words like milites, pauperes, maiores, mediocres and plebs meant different things to different people. This is made clear by Kostick, who devotes a full third of his book to a careful and enlightening exposition of his major authors. If Raymond of Aguilers, for example, has a ‘distinctive vocabulary’ which makes him use principes in a way that is broader than others, how much precision can be employed in analysing who the principes were? And the problem goes deeper, because as Kostick shows, Raymond attaches three or even four different meanings to pauperes, depending on circumstances. So the ground shifts all the time. In practice, therefore, reconstructing the social configuration of the First Crusade with exactitude is a hopeless task. But this does not mean that Kostick's approach should not be applied to later expeditions, when European society had become more stable. Nor does it rob this book of value. By rereading the narrative accounts (curiously, the surviving letters are largely ignored) with his attention fixed on social origins, he is able to throw interesting light on some of the crusade's central problems and episodes, including the recuitment of the pauperes, the career of the visionary Peter Bartholomew, and the application of ius in bello following the capture of Jerusalem. He provides a stimulating analysis of the iuvenes, deploying Georges Duby's classic essay, and there is a useful chapter on women as crusaders, a field of study that is currently very active. The book has not been attentively proof-read and there are an unfortunate number of misspellings and inconsistencies, but it constitutes a worthwhile and laudable attempt to approach early crusading from an angle that is usually overlooked.