The geology of the Western Front had an enormous impact on how military operations were carried out, determining the strength of trench walls, whether tunnels could be dug under no man’s land, if tanks could proceed without sinking into mud, even the size of craters after shell explosions. This survey examines how the terrain and topography of Flanders, Artois and Picardy, including soil and rock formations, influenced military strategy during the First World War.