This book has had a long genesis. In 1967 I started work on an Oxford D.Phil. thesis under the supervision of the late G.D.G. Hall. My original intention was to work on the Leges Henrici Primi, but Derek did not think it was a suitable topic for a postgraduate thesis and suggested that there was another topic I might like to work on. It was a problem that had arisen out of his own current work on dating registers of writs for the Selden Society edition of Early Registers which had been begun by Elsa de Haas but which he was then completing. This was the extent to which the Provisions of Westminster of 1259 (or the reissues of 1263 and 1264) had ever been enforced in the courts or in other ways between 1259 and the final reissue of the Provisions as the Statute of Marlborough in 1267. This turned out to be a little too narrow a focus for a doctoral thesis. So we agreed to broaden it out to a more general consideration of the genesis and background of the legislation and its enforcement not just between 1259 and 1267 but also between 1267 and the end of the reign of Edward I in 1307. There was much less pressure then to finish doctoral theses within a three-year period and I did in fact not complete and submit the thesis until 1974. The thesis benefited considerably from the delay.