thumb|200px|A Weaver rail
A Weaver rail mount is a system to connect telescopic sights (often via a scope mount) and other accessories to firearms and certain crossbows. It uses a pair of parallel rails and several slots perpendicular to these rails.
The later Picatinny rail, developed by the US military, is a development of the key concepts of the Weaver system, and they are partially compatible.
History
The Weaver mount was developed by William Ralph Weaver (1905 – 8 November 1975) at his telescopic sight company W.R. Weaver Co., which he founded in 1930. Previous systems included the Leupold/Redfield mounts. Compared to the Leupold mount, the Weaver rail is not as strong and cannot be adjusted for windage. Because of this, with devices that use only one locking slot, Weaver devices will fit on Picatinny rails, but Picatinny devices will not always fit on Weaver rails.