A rail integration system is a generic term for a standardized system for attaching accessories to firearms. Rail systems are straight mounting brackets on the gun's receiver, handguard, or fore-end stock to allow sliding or variable-position attachments. An advantage of the multiple rail slots is the moveable positions to adjust for optimal placement of each item for a user's preferences, along with the ability to switch different items at different placements due to varying eye reliefs on gun sights.

A Weaver rail mount is a system to connect telescopic sights and other accessories to firearms and certain crossbows. It uses a pair of parallel rails and several slots perpendicular to these rails.