Leica introduced the R system in 1964 as an alternative to their M mount rangefinders and as a response to the successful SLR systems of the time, including Nikon F and Pentax M42. The R system was produced, with some modifications, until 2009.

Most R mount lenses can be used on any R mount camera, but there are compatibility issues with both the oldest and newest lenses. Over time, Leica added features and technology to the lenses that made them incompatible.