This paper reviews fuel-saving technologies for commercial trailers, provides an overview of the trailer market in the U.S., and explores options for policy measures at the federal level that can promote the development and deployment of trailers with improved efficiency. For trailer aerodynamics, there are many technologies that exist and are in development to target each of the three primary areas where drag occurs: 1) the tractor-trailer gap, 2) the side and underbody of the trailer, and 3) the rear end of the trailer. In addition, there are tire technologies and weight reduction opportunities for trailers, which can lead to reduced rolling resistance and inertial loss. As with the commercial vehicle sector, the trailer market is diverse, and there are a variety of sizes and configurations that are employed to meet a wide range of freight demands. Despite this great diversity, box-type vans represent more than two-thirds of the sales market and likely constitute a large percentage of total trailer miles traveled. In terms of manufacturing and sales, the trailer market is fairly consolidated, with the largest five companies accounting for nearly two-thirds of total sales. The van trailer marker is even more consolidated, with the top five companies making up more than 90 percent of total sales. As policymakers in the United States and across North America weigh options for trailer policy measures, the authors recommend integration of trailers into the Phase 2 U.S. heavy-duty vehicle regulatory program, with emphasis on box trailers but inclusion of other types as well.