Joan Thirsk was a distinguished historian of the early modern society and economy, and especially of agriculture who was formerly based in the then Department of English Local History. Her greatest achievement as an agrarian historian was to explore and define the regional differences that everyone thought important but which few could define. At Leicester in the 1950s a scheme for an Agrarian History of England and Wales was developed, and was driven forward by H.P.R. Finberg, who had succeeded W. G. Hoskins as the head of the Department of English Local History. Joan Thirsk devised a strategy for writing volume 4 of the series, devoted to the period 1500-1640, with such success that it was published in 1967, well ahead of the other volumes. She realised the importance of reflecting in the new volume the variety of the English regions, and a modest amount of funding allowed researchers to be employed to gather documentation from all over England. In particular the probate inventories were systematically calendared and summarised, which provided the best evidence for crops, animals and equipment, and therefore allowed the different farming systems to be identified.
Joan Thirsk went on to a post in Oxford, edited vol. 5 of the Agrarian History, and researched new subject such as economic projects (including woad cultivation), alternative agriculture (which deals with new products such as tobacco and llamas), and then early modern food. Thirsk deposited the data collected for the Agrarian History volumes 4 and 5 (5 boxes in total) in Special Collections in the David Wilson Library. The Joan Thirsk Collection provides researchers with the opportunity to make use of a carefully assembled and meticulously transcribed set of records. They contain information which could be used for new investigations, for example into the layout of houses and the types of farm building, of which only limited use was made in the completed Agarian History volumes.