It is impossible to understand how the medieval church functioned -- and in turn influenced and controlled the lay world within its care -- without understanding the development, character and impact of `canon law', its own distinctive law code. However important, this can seem a daunting subject to non-specialists. They have long needed an attractive but authoritative introduction, avoiding arid technicalities and setting the subject in its widest context. James Brundage's marvellously fluent and accessible book is the perfect answer: it will be warmly welcomed by medievalists and students of ecclesiastical and legal history.