Leica was technically one of the earliest entrants in the mirrorless camera race (2006), as they simply transitioned their existing M-mount film camera to digital with the M8.
The M series are a bit different than most later mirrorless cameras in that the M-mount Leicas use an optical rangefinder (manual focusing) and they don't rely upon Live View on the rear LCD or an EVF to compose. Later variations of the M (9, M-E, Monochrom, 240, etc.) are full frame, while the original M8 is APS sensor size.
In 2014 Leica introduced a second mirrorless camera type based around an APS sensor, the T, which uses a new set of new L-mount autofocus lenses (though it can use Leica M-mount lenses via an adapter).
In 2015 Leica introduced yet another mirrorless camera, the SL, once again based around a full frame sensor and using the L mount.
The T (and now TL2), CL, and the SL2 share a lens mount, the L-mount, with CL/TL lenses being crop-sensor lenses mostly to be used with the TL and CL models, and SL lenses being full frame lenses that can be used with all L cameras. Panasonic and Sigma also make L-mount lenses.
Here is the full set of current Leica mirrorless cameras, with complete data for each:
For older Leica cameras, click here. Note that I'm more aggressive than Leica in defining "current" cameras. Leica tends to continue making a low volume of older cameras even after the replacement is created.
Available Leica L (SL, TL) Mount Lenses
