The department of Aisne is surrounded by the French departments of Nord, Somme, Oise, Ardennes, and Seine-et-Marne and borders Belgium to the northeast. The Aisne River crosses the area from east to west, where it joins the Oise River. The Marne forms part of the southern boundary of the department with the department of Seine-et-Marne. The southern part of the department is the geographical region known as "la Brie poilleuse", a drier plateau known for its dairy products and Brie cheese.