The ASCEND program supports the development of novel lightweight and ultra-efficient electric motors, drives, and associated thermal management system (collectively referred to as the all-electric powertrain) that will facilitate net-zero carbon emissions in the single-aisle, 150-200 passenger commercial aircraft segment. This FOA represents part of a wider ARPA-E effort in the development of enabling technologies for long-range (≥ 2,800 nautical miles), carbon neutral commercial aviation. The other part of the wider ARPA-E effort is included in a separate FOA targeting ultra-efficient and lightweight energy storage and fuel-to-electric power conversion system (REEACH). The overarching goal of the two FOAs is to reduce the emissions from commercial aviation by developing cost-competitive systems for the efficient conversion of the chemical energy of carbon-neutral liquid fuels (CNLFs) to delivered electric energy, which is then further converted to thrust via propulsors driven by electric motors and associated motor drives. The focus of the ASCEND program is the development of an all-electric powertrain as the prime mover for long-range, narrow-body aircraft such as the Boeing 737. Current electric powertrains do not have high enough power density and efficiency to enable competitive and fully decarbonized aviation for the narrow-body class of aircraft. The ASCEND program aims to take advantage of emerging materials, manufacturing techniques, and design topologies, with a focus on the co-design of electromagnetics, power electronics, and thermal management solutions. The ASCEND program requires demanding figures of merit for specific power (greater than or equal to 12 kW/kg) and efficiency (greater than or equal to 93%) for the fully integrated all-electric powertrain systems; these targets, among others, are well beyond the capability of current state-of-the-art technologies and will require creative thinking and innovation in the electric motor and power electronics space.