International audience This article provides a summary of research activities and outcomes following several years of aerial and ground-based surveys undertaken at Koh Ker, in Preah Vihear Province in northwest Cambodia. Key findings include the discovery of a sophisticated and multi- period system of hydraulic engineering works bearing some similarities to that of Angkor in the 10th century ; the identification of areas likely devoted to intensive agriculture during the Angkorian period ; a re-appraisal of previously identified "roadways" and "city enclosures" ; evidence for domestic habitation and stone working sites ; the degree of connectivity of the northern "road" from Koh Ker to the Beng Mealea to Vat Phu road ; possible continuity of occupation from early historic to post-Angkorian periods ; evidence for the collapse of the water management system ; and indications of large-scale changes to the local environment including alterations in the flows of entire river systems.