A U.S. nation-wide transmission overlay is a high capacity, multi-regional transmission grid, potentially spanning all three interconnections, designed as a single integrated system to provide economic and environmental benefits to the nation. The objective of this paper is to identify benefits to building a national transmission overlay and to lay out essential elements to facilitate continued dialog on this topic. A preliminary study performed on a national scale using a long term investment planning software illustrated that a national transmission overlay, under a high renewable penetration scenario, could result in cost-reduction of between one quarter trillion and one-half trillion dollars over a 40-year period, while promising to increase infrastructure resilience and flexibility. (C) 2013 Elsevier Ltd. All rights reserved.