The Pentacon Six or P6 is a breech-lock bayonet lens mount used by several 6x6 medium format single-lens reflex cameras from East Germany and the Soviet Union. The P6 mount was created by Kamera Werkstätten and Carl Zeiss Jena for the Praktisix camera but the mount has become more associated with the Pentacon Six name. Pentacon Six cameras were manufactured from the mid-1950s to the early 1990s with very few changes. 

An exceptionally wide range of lenses is available in the Pentacon Six mount and some are among the best lenses ever made for medium format cameras, like the Carl Zeiss Jena 50mm F4 Flektogon, the 180mm f2.8 Sonnar and the Schneider-Kreuznach 80mm F2.8 Xenotar.