Ford studied lean NO_x traps (LNTs) extensively for over 20 years and used LNTs successfully on both lean burn gasoline and diesel vehicles. Three-way catalysts (TWCs) are remarkable devices that control vehicle emissions of carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NO_x) with 99.9% effectiveness; however, TWCs do not provide suitable NO_x control under lean exhaust conditions. The design and management of LNTs, especially during sulfur removal, is of upmost importance for overall functionality and durability. The maximum thermal limit of LNTs was increased while the deSO_x temperature was decreased, enabling their implementation with improved controls. LNTs can generate ammonia, so they are often combined in diesel exhaust systems with selective catalytic reduction (SCR) catalysts or SCR coated diesel particulate filters (SDPFs), providing NO_x control during more types of driving conditions than LNT alone. The use of LNTs on gasoline is far less widespread. Despite all the efforts on lean NO_x control for gasoline vehicles, the fuel benefits are not enough to justify the extra cost of additional catalysts and associated sensors. This case study summarizes the operational, functional, and compositional differences between LNTs applied to gasoline and diesel vehicles, and what drives the decision for an automaker to choose a particular system.