The Rektoratskirche St. Karl Borromäus, commonly called the Karlskirche (German for 'St. Charles Church'), is a Baroque church located on the south side of Karlsplatz in Vienna, Austria. Widely considered the most outstanding baroque church in Vienna, as well as one of the city's greatest buildings, the church is dedicated to Saint Charles Borromeo, one of the great counter-reformers of the sixteenth century.

Located just outside of Innere Stadt in Wieden, approximately 200 meters outside the Ringstraße, the church contains a dome in the form of an elongated ellipsoid.