Designed to fill a long-standing gap in the literature, this is a notably well-written and lucid introduction to the subject, aimed particularly at graduate students, archivists, historians, archaeologists - anyone with a special interest in medieval documents or artefacts. It is illustrated with over 120 high-quality reproductions, mainly of seals from the very extensive collections in The British Library and Public Record Office, London, each accompanied by a detailed caption, including the seal's actual dimensions. The authors discuss every kind of seal used for authenticating documents - their development, their design, their use - with a host of references to contemporary records. An index of mottoes and inscriptions provides invaluable and practical help to identifying seals in other collections.