Laxenburg (Central Bavarian: Laxnbuag) is a market town in the district of Mödling, in the Austrian state of Lower Austria.

Located about 20 km (12 mi) south of the Austrian capital Vienna, it is chiefly known for the Laxenburg castles, which, beside Schönbrunn, served as the most important summer retreat of the Habsburg monarchs.

Duke Albert III (1349–1395) had a hunting lodge erected here (today called Altes Schloss) and vested the settlement with market rights.

Rebuilt in a Baroque style by the master builder Lodovico Burnacini, it became the centre of extended gardens and pleasure grounds.

Later Empress Maria Theresa acquired the palace and from 1756 onwards had it lavishly rebuilt by her court architect Nicolò Pacassi with a Rococo interior.

Since 1973, the International Institute for Applied Systems Analysis (IIASA), a non-governmental research organization with about 200 employees, has been located in the castle.