In 2018 Leica formed the L-Mount Alliance, licensing Sigma, Panasonic in the same year, to use an upgraded version of the mount for their own products, opening the way for a more extensive system of fully compatible cameras and lenses.

[3] Ernst Leitz Wetzlar GmbH, the cine lens business of Leica, joined the L-Mount Alliance in 2021,[4] DJI followed in 2022,[5] Samyang, Astrodesign[6] and Blackmagic Design in 2023.

At the time of introduction, it was called the "T-mount", but this was changed to "L-mount" with the release of the Leica SL, a full-frame sensor camera using the same mount.

On 25 September 2018, the L-Mount Alliance between Leica, Panasonic and Sigma was announced, enabling the partners "to make use of the L-Mount standard developed by Leica for their own developments and to offer both cameras and lenses utilising this lens mount" with full compatibility between the three companies' products.

[19] Panasonic committed to releasing a total of ten lenses for the L-mount by the end of 2020, beginning with the 50mm F/1.4 prime and the two zooms listed below; stating that they would provide details at Photokina 2019.

14 primes from Sigma's 'Global Vision' range, primarily designed for reflex cameras with short flange depths and currently available for the mirrorless Sony E-mount, will also be released in L-Mount from 2019.