This thesis is a study of the Berkeley family through five generations from 1281 to 1417 and attempts to study in depth all the aspects of their lives for which material is available. This is far more abundant for the Berkeley family than for many others in a similar position in the late middle ages which makes them a suitable subject for such study. The first lord in the series is Thomas II (lord 1281-1321) who had a personal association with Edward I manifested in his close involvement in all the most important events of the reign. He virtually retired from active public life during the reign of Edward II and his heir, Maurice III (1321-26), took over as representative of the family. He benefited from the lordship of the earl of Pembroke which brought him several important posts between 1312 and 1318, but he then broke with Pembroke to join the Marcher opposition to the king. He was one of the leaders of the rebels in the Despenser War of 1321-2 and spent the rest of his life imprisoned at Wallingford. His son, Thomas III (1326-61), was married to Mortimer's daughter and consequently played an important role during the Mortimer regime, but suffered an eclipse during the 1330s while undergoing his parliamentary trial for the death of Edward II. He re-emerged onto the national stage in the 1340s but was principally concerned with domestic and estate matters. His heir, Maurice IV (1361-68) was retained by the Black Prince and was wounded and captured while in the Prince's service at Poitiers. The wound made him an invalid for the rest of his life and he was further hampered by the burden of paying off his ransom. His son Thomas IV (1368-1417) was a minor until 1374 and then was severely restricted financially by the claims on the estate of two long-lived dowagers until 1390. This was to ascertain extent mitigated by the fortuitous inheritence by his wife of the Lisle estate but he played no important role in the affairs of Richard II's reign. He was prominent, however, in the establishment of Henry IV in 1399 and was a Privy Councillor of that king until 1406 when he appears to have been dropped when Prince Henry's influence at court became important. These activities at court were influenced principally by the lords' personal associations with the current ruler and in normal circumstances they did, not have the status consonant with the right to involvement in affairs of the highest importance. They were, however, at the highest end of the peerage since their income rose to almost comital size and this position was enhanced by marriage alliances with other peerage families of similar high incomes and long establishment. The daughters of the family, however, occasionally married men of lesser status. Portions, jointures and dowers were distributed and received in conformity with the general rules governing such matters but the most prominent and important of their family relations was the loyalty shown by the cadets to Gloucestershire and the main line. This was occasionally of particular importance, such as the alliance between Thomas III and his courtier brother, Maurice (of Stoke Giffard), but was at all times a source of great strength to the lords whose influence in their "country" was thereby greatly extended. A second major factor in the Berkeley lords' dominance of their "country" (which appears to have been, in most respects, the county of Gloucestershire) was the concentration of their estate in that area. This was improved by the acquisition of new lands in the same area and although most of these lands were subsequently granted to younger sons, these cadet branches only served to strengthen the lords' position further. The income derived from that part of the estate which descended with the main line rose from around £900 per annum in the late 13th century to £1,150 per annum by 1360 but on occasions it was considerably higher than this, notably after the Lisle lands came to Thomas IV in 1382 and 1392. Although the, lords' resources, and their ability to concentrate all of them on the one area, was an important element of their influence in the county, a more important factor, perhaps, was the lack of any serious rivals within Gloucestershire. This enabled the Berkeleys to have what amounted to almost a monopoly of lordship and a great deal of influence over appointments to local offices. Their increasing stature is reflected in the changing methods they adopted to impose their will in the area, these growing in sophistication over the period. Their lordship was reciprocated-by the members of their affinity who assisted and supported them in their various endeavours. Detailed study of the manor of Ham (the largest of those making up the honour of Berkeley) showed that there was a huge increase in the number of tenements held by free tenants, and in the rents paid by them, under the lordship of Thomas II. He also cut down the number of villein tenements, the profit from which was restricted by custom, but the principal change in this respect occured after the Black Death when many tenements came to be "held freely" for a greatly increased cash rent. The adverse effects of the Black Death were quickly corrected in the short term but long term effects are apparent in the static nature of the rent-roll from 1360. The use and type of labour changed over the period since Thomas II was content to have a smaller number of famuli and make greater use of villein labour services, while Thomas III used much of the villein labour obligation to support famuli (thus increasing the numbers employed) and making up the deficit with casual labour. Most of the stock on the manor were draught animals and, although many went to the household, sale became more important after 1360 as policy changed it into more of a "cash" manor. There was a large demesne which produced great quantities of wheat and oats and smaller quantities of beans, most of which went to the household. The lords' followed most of the agricultural techniques advised in the treatises but on matters not covered by them, the local wisdom which predominated was not as helpful as it could have been.