The Church of St. Leopold in Vienna is one of the most famous Art Nouveau churches in the world. The church, situated 310 metres above sea level, dominates and forms part of the Steinhof Psychiatric Hospital is located on a hillside below the Galitzinberg in the 14th Vienna district, Penzing. It was built in 1903-1907 by the 63-year-old architect Otto Wagner, with mosaics and stained glass by Koloman Moser, and sculptural angels by Othmar Schimkowitz (1864 - 1947). The great majority of the other smaller details are the work of Otto Wagner himself. The statues on the two external towers represent Saint Leopold and Saint Severin (l. & r. respectively: they are the two patron saints of Lower Austria) and are the work of the Viennese sculptor Richard Luksch (1872 - 1936).

Unusually the church lies on a North-South axis, at the centre-top of the hospital complex. Otto Wagner incorporated numerous features specifically related to its function within an asylum: e.g. there are very few sharp edges, and most corners are rounded; almost no crosses are visible; the priest's area is potentially entirely separate from the patients'; access to the pulpit is only from the vestry; emergency exits are built into the side walls in case a patient needed to be speedily removed; continuously flowing water replaced holy water stoups at the entrance; there were separate entrances for male and female patients; confessionals were more open than is customary. The elaborate and brightly-coloured mosaic behind the ornate altar represents the reception of the departed soul into heaven, via an ornate trompe-l'oeil staircase which has been compared unfairly to a Hollywood-style movie award ceremony. Among the numerous saints attending the ceremony is Saint Dymphna the patron saint of those afflicted by epilepsy or mental illness. Also visible is St. Clement Hofbauer or Clemens Maria Hofbauer (1751 - 1820), the patron saint of Vienna.