The Leica M mount system was introduced in 1954 alongside its first camera, the M3. The M's bayonet system was a drastic improvement over previous screw-mount Leica cameras. The M system is faster, with better quality lenses and bodies. Viewfinders were bigger and brighter, with coupled framelines and rangefinders for achieving perfect focus quickly. The cameras were quiet, robust, and reliable and quickly became the camera of choice for professionals like Henri Cartier-Bresson.
Even though lens quality improved in the M era, Leica introduced a number of adapters that would allow screw mount lenses to work perfectly on M bodies, even bringing up the right framelines in the viewfinder.
Most Leica M film cameras are mechanical and do not require batteries to function. The M6, M7, and CL are the only exceptions, losing some or all functionality when the batteries are removed. The Leica MP is one of the only 35mm film cameras still available, new.
Leica lenses are among the best in the world, and their optical designs have stood the test of time over the past 60 years. They provide excellent contrast, resolution, structure and tonal depth, while retaining a classic character that many pros prefer to the clinical sharpness of Canon or Nikon lenses. Build quality of Leica lenses is exceptional.
Leica M mount has also been used by other camera and lens manufacturers, such as Cosina Voigtländer, Carl Zeiss, Konica, and Minolta.