Transportation in the United States faces significant challenges, including uncertain funding, congestion, unsustainable trends in energy consumption and greenhouse gas (GHG) emissions, and high costs to households and government. Ridesharing represents a cost-effective option for addressing many of these concerns. Although ridesharing has declined in recent decades, it continues to play an important role in the transportation system today, and new developments such as social media present opportunities to increase ridesharing nationwide. This paper examines the role and potential of ridesharing, specifically carpooling and vanpooling (C/V), in the U.S. transportation system, and concludes that ridesharing merits greater support from federal, state and local transportation agencies.