Abstract: Disclosed herein are embodiments of stair lift systems arranged such that a number of configurable subcomponents can be assembled to form a wide variety of stair lift systems that meet the spatial, dimensional, and physical arrangement of an equally wide variety of pre-existing stairways and staircases in residential and commercial settings. Each embodiment of a stair lift system is highly configurable, can generally be installed in one session, and provides enhanced and additional functionality as compared to prior art stair lift systems. A stair lift system generally comprises a modular and configurable rail assembly, a plurality of modular and configurable post assemblies for securing the rail assembly to the pre-existing staircase, and a chair that engages with and traverses the modular rail assembly to move a user up and down the staircase.