During 2004–2005 Oxford Archaeology carried out a series of archaeological excavations along the proposed route of the A421 Great Barford Bypass, Bedfordshire (NGR TL 102 513–TL 159 554). The route extends from the Black Cat roundabout on the A1 and runs to the north and west of Great Barford linking up at its western end to the A421 Bedford Southern Bypass near Water End. A total of nine sites (Sites 1–9) were investigated in detail revealing evidence of activity from early prehistoric times through to the post-medieval period. Earlier prehistoric activity was sparse and largely evidenced through a light flint scatter over the entire route and a single early Neolithic pit on Site 2. Isolated early Bronze Age pits were located at Sites 2 and 6. Following an apparent hiatus in the middle Bronze Age small-scale activity reappeared at Site 2 in the later Bronze Age-early Iron Age. More widespread occupation and associated activities were apparent from the middle Iron Age and have been documented at Sites 2, 4, 6 and 7. Three of these sites (2, 4 and 6) continued to be occupied into the later Iron Age. By the early Roman period Site 6 had become abandoned shortly followed by Site 2, but activity was still evident at Sites 1, 4, 7 and 8. Of these only Site 8 continued to be inhabited into the later Roman period, although a late Roman cemetery was excavated at Site 4, suggesting continued occupation nearby. Site 8 also saw some post-Roman activity as did the adjacent site at Site 9 where a small hamlet was established in the late Saxon/early medieval period possibly over an earlier mid-late Saxon settlement. Two new sites (Sites 3 and 5) saw small settlements established dating to the 10th–13th and 12th centuries respectively.