The Département de l’Aisne (02) is in northeastern France. Most of it lies in the northeast of the Paris basin, but the northwestern region around St Quentin lies on the upper Somme, which rises near that town. Two major tributaries of the Seine flow westwards across the department: the Oise in the north and the Marne, in the area around Château Thierry in the south. The name-giving Aisne, a tributary of the Oise, flows through the centre, past the town of Soissons. Laon, the capital, is between the valleys of the Aisne and Oise.
Most of the department was formed in 1790 from eastern Picardy and the northeast of the Île de France. Though in different gouvernements, these areas had been under the same intendant as part of the généralité of Soissons. The southern district around Château Thierry however had belonged to Champagne and to the généralité of Châlons. In the early Middle Ages this whole region had been a conglomeration of lordships, many important, and most of which came into royal hands well before the coming of the Renaissance.
The department contained two longstanding episcopal cities. Soissons was preferred to Laon, with its hill-top cathedral, as the seat of the Bishop, but Laon became the capital. The sub-prefectures for the other arrondissements are St Quentin, Soissons, Vervins (in the northeast) and Chateau Thierry (with an interruption, 1926-42).
During the Second World War the department was in the occupied zone from 1940. The north, including Laon, lay in the zone interdite, to which those who had fled as refugees in 1940, were forbidden to return. In 1941 the Vichy régime made the Prefect of the Aisne the Regional Prefect with responsibility in police and economic matters for a region of four departments: Aisne, Ardennnes, Somme, and Oise.
Since 1960 the department has belonged, with the Somme and the Oise, to the Picardie region.