The North Sea has reached an ultra-mature state as a petroleum basin, entering a phase of infrastructure-led exploration in an attempt to extend the economic lives of the main fields and reduce the rate of production decline. At the same time, the transition to a future low-carbon use of the basin is also in progress. As the papers in this volume demonstrate, in order to find, appraise and develop the mostly smaller near-field opportunities as well as making sure to grasp the opportunities of the near-future energy transition, a regional understanding of the North Sea is still critical. Even more so, a cross-border approach is essential because: (1) some of the plays currently being targeted have a clear cross-border element; (2) it allows a comparison of stratigraphic names throughout the entire basin; and (3) it enables explorers to learn lessons from one part of the rift to be applied somewhere else. This volume offers an up-to-date ‘geology-without-borders’ view of the stratigraphy, sedimentology, tectonics and oil-and-gas exploration trends of the entire North Sea Basin. The challenges associated with data continuity and nomenclature differences across median lines are discussed and mitigated. Examples of under-exploited cross-border plays and discoveries are discussed.