Musicians of the 18th century were, by and large, pragmatists. Contemporary documents are also available that shed light on Viennese performances of Wolfgang Amadeus Mozart's dances and sacred works. By investigating sets of performance parts from Mozart's estate, it is even possible to make informed guesses about the sizes of the orchestras in his public and private concerts—events which are otherwise poorly documented. This chapter discusses Viennese orchestras that performed Mozart's works during his lifetime, focusing particularly on orchestral size and balance. Mozart's Viennese concerts were held not only in the Burgtheater and the Kärntnertortheater, but also in the Mehlgrube, in the casino in the Trattnerhof, in Jahn's restaurant in the Himmelpfortgasse, in the Augarten, in public squares, in Masonic lodges and in a wide variety of private residences. Few performances of Mozart's sacred works are known with certainty to have taken place in Vienna during his lifetime.