Opposed-piston (OP) engines have attracted the interest of the automotive industry in recent years because of their potential for significantly improved fuel economy. Opposed-piston, two-stroke (OP2S) engine technology amplifies this fuel efficiency advantage and offers lower cost and weight due to fewer parts.While OP engines can help automotive manufacturers comply with current, and future, efficiency standards, there is still work required to prepare the engines for production. This work is mainly related to packaging and durability.At Achates Power, the OP2S technology is being developed for various applications such as commercial vehicles (heavy-and medium-duty), SUVs, pick-up trucks and passenger cars (i.e. light-duty), military vehicles, large ships and stationary power (generator sets).Included in this paper is a review of the previously published OP engine efficiency advantages (thermodynamics, combustion and air system) as well as the architecture's historical challenges. Also included is: 1An overview of the packaging-related challenges of OP2S engines using opportunities with the dual-crank, Junkers Jumo-style design with power take-out options, vertical engine installation and bore-to-bore distance.2Different design parameters of the OP2S engine and their optimization for various applications.3Details of OP2S engines for various applications, including packaging concepts and performance and emissions results.These results suggest that the technology is ready to produce an economically and environmentally sustainable OP powertrain-one that is clean, fuel efficient and can fit into existing vehicles, be manufactured in today's engine plants, and run on a variety of fuels.