Schloss Klessheim is a Baroque palace located in Wals-Siezenheim, 4 km (2.5 mi) west of Salzburg, Austria. The palace was designed and constructed by Austrian architect Johann Bernhard Fischer von Erlach for Prince-Archbishop Johann Ernst von Thun in 1700. It became the summer residence of the Archbishops of Salzburg. Since 1993, the palace has been used by Salzburg Casino.

Johann Bernhard Fischer von Erlach was an Austrian architect, sculptor, engraver, and architectural historian whose Baroque architecture profoundly influenced and shaped the tastes of the Habsburg Empire. His influential book A Plan of Civil and Historical Architecture (1721) was one of the first and most popular comparative studies of world architecture. His major works include Schönbrunn Palace, Karlskirche, and the Austrian National Library in Vienna, and Schloss Klessheim, Holy Trinity Church, and the Kollegienkirche in Salzburg.