Technically this is the third edition of a book first published in 1954 and revised for a paperback edition (which cost five shillings) in 1962. When it was originally written over thirty years ago, I and all the world were young, and there were few in the field of castle studies. Since then there has been a considerable and continuing revival of academic interest in the subject, not least in this country, in France and in Germany. As instances, which could be multiplied, the History of the King's Works has been written for the medieval centuries (1963); a series of bi-annual European conferences on Castellologie, of which the eighth will be held this summer, has been established (under the name of ‘Château-Gaillard’ because the first and most memorable of the conferences was held there, at Les Andelys, in 1962); and a research project into the origin of the castle has been launched and largely completed by the Royal Archaeological Institute. In view of all this activity it seemed necessary substantially to rewrite a large part of my book, especially the earlier chapters, to incorporate recent work: at least the first half of it is therefore new, as also are all the notes, which have now become very necessary, and many of the illustrations. Nevertheless, it is satisfying to report that the message even of the earlier chapters is what it was before, albeit presented with much more scholarly detail and with much more reference to France, whence came our castles and our feudalism. These, indeed, are the basic facts which stand, namely that castles are feudal, and in this country are, with feudalism itself, a Norman and French innovation, part and parcel of the Norman Conquest. As for the type of these early castles on both sides of the Channel, while it is nowadays emphasized that not all of them had mottes, and while it ought to be emphasized that not all of them were of earthwork and timber, it remains a certainty that the ‘motte-and-bailey’ castle was already well established in France and Normandy before 1066 and came to England thence.