The Leica M3 is a 35 mm rangefinder camera by Ernst Leitz GmbH (now Leica Camera AG), introduced in 1954. It was a new starting point for Leitz, which until then had only produced screw-mount Leica cameras that were incremental improvements to its original Leica (Ur-Leica). The M3 introduced several features to the Leica, among them the combination of viewfinder and rangefinder in one bright window, like on the Contax II, and a bayonet lens mount. It was the most successful model of the M series, with over 220,000 units sold by the time production of the M3 model ended in 1966.

It was succeeded by a number of later M series cameras, including the M7 film camera which is still in production today (Wikipedia).

The Dual Range Summicron f/2 lens came with an auxiliary fitting similar to that of the 35mm "specs" attachment with a lens & prism to fit over the view and focus windows. It was used when the camera to subject distance was from the near range minimum of about 18 inches (0.5 meters) to the maximum of 36 inches (0.9 meters). These auxiliary "specs" were removed when focusing in the regular range beyond 36 inches. The Summicron lens could not turn to the near range settings unless the auxiliary "specs" were fitted in place on the lens.

Early M3s had a double stroke advance lever, like the Neoca 2s would. Later models (from model no 915 251) had single-stroke levers, which quickened up operation of the camera.

Early models used a glass plate to keep the film flat; later models used a metal plate.

Loading of the film is done by removing the bottom plate, like on the Leica II and III series; A Door flap on the rear of the camera can be raised, allowing for easier access to the film and overcoming a problem associated with these earlier screw lens fitting Leicas. The film is inserted from the bottom of the camera pre-attached to the take-up spool. Special cassettes were also available. (Wikipedia).