While I was staying in Cambridge as a Visiting Fellow of University College, whose warm hospitality I would like to acknowledge, the Faculty of History invited me to give a series of four lectures. I accepted the invitation with pleasure and the Faculty agreed that I should talk of the formative years of the Common Law of England. I felt that the students might find it useful to hear, in the succinct and – I hope – accessible form of lectures, some views I had expounded in a more elaborate and detailed way in my Royal Writs in England from the Conquest to Glanvill (London, 1959). I also welcomed the opportunity to air some new views which I was working on at the time in the quiet of Cambridge's fine libraries. When eventually the University Press invited me to publish the lectures, I gladly welcomed the occasion to place them at the disposal of the wider reading public.

Certain themes of my Cambridge lectures I treated subsequently in Newcastle, Oxford, Paris and Tübingen, where I profited greatly from discussions with learned historians and lawyers, as I had done in Cambridge: for this I offer them my warmest thanks. My text has been expanded, brought up to date and annotated, but follows closely the original pattern of the four lectures as they were given in the spring of 1968.