Professor Oosthuizen's research focuses on three main topics:

• The evolution and transformation of early medieval and medieval fields and pastures from the landscapes of Roman Britain, many of which had much more ancient origins;
• Detailed regional studies of English rural settlement and husbandry between c.400–c.1300;
• Conceptual approaches to the archaeology of collective organisation in agriculture, not only in shared fields but also in natural resources exploited under rights of common.

Her most recent research on the Emergence of the English (forthcoming, see below) draws on all three threads. It argues that the origins of that process should be sought among the prehistoric communities and territories that had developed across England through the period of Roman control and into subsequent post-imperial decades and centuries. Remarkable continuity across the longue durée between the early fifth and the seventeenth centuries in the ecology and geography of many areas exploited under rights of common property –  often also the basis of equally long-enduring political or administrative units - suggests that most change was either short-lived and/or adaptive and evolutionary, rather than characterized by any sudden revolutionary transformation. That rich and complex history reveals a traditional society assimilating newcomers, and continually evolving, adapting and innovating in response to individual and collective actions, to events, small- or large-scale, sudden or expected, and to local, regional and international influences and processes, new or familiar, rapid or slow.