The Laon Cathedral in the old town was begun in the second half of the 12th century and completed in 1235. Adjoining the cathedral is a 13th-century cloister. The nearby Episcopal Palace (partly 13th century) now houses law courts and has a 12th-century chapel. On the cathedral's other side lies a 13th-century abbey with a large underground Gothic hall, now a hospital. The Museum of Laon has a collection of Roman and medieval jewelry. It also contains paintings by the three brothers Le Nain, 17th-century painters who were born in Laon. A 12th-century octagonal Chapel of the Templars stands in the museum gardens. The old town has a monument to the explorer Jacques Marquette, also born in Laon.

The hilly district of Laon (Latin: Laudunum) has always been of some strategic importance and was fortified by the Romans. At the end of the 5th century, Saint-Rémi, archbishop of Reims (Remigius of Reims, Saint), instituted a bishopric in the town, and it remained a religious and intellectual centre until the Renaissance. Laon was the medieval capital of the Carolingian (Carolingian dynasty) kings. Hugh Capet, however, who became king in 987, seized the town with the connivance of the local bishop and then moved the capital to Paris. In the 12th century Laon revolted against the authority of the bishops, but Louis VI quashed the rebellion. During the Hundred Years' War (1337–1453) Laon changed hands a number of times but was finally retaken by the French king. The bishopric was abolished in 1790 during the French Revolution. In 1870, when the Germans invaded, an engineer blew up the powder magazine, killing 500 people and damaging the cathedral. Laon was occupied during World Wars I and II, and the new town was severely damaged in 1944.

Laon is an administrative centre and minor industrial town that has benefited from the decentralization of Paris. The main industries include printing and the manufacture of cables, clothing, heating equipment, and plastics. Pop. (1999) town, 26,265; (2005 est.) 26,600.