The Large Scale Networking Interagency Working Group held an Operationalizing Software-Defined Networks Workshop on September 18-20, 2017, in Washington, DC. At this workshop, Federal, private, and academic stakeholders discussed the current state-of-the-art and path forward to realize an open, innovative, multidomain, and interoperable software-defined network (SDN) as an operational infrastructure that can rapidly adjust to the evolving communication and computing needs of science, engineering, and commerce, while simultaneously enhancing the economics, security, evolution, and manageability of the network.The Operationalizing Software-Defined Networks Report discusses SDN adoption and identification of key areas for further exploration, focusing on flexibly enabling end-to-end paths to network, compute, and storage resources with customizable properties, using software to easily assemble such paths across hardware infrastructure, with favorable economics, security, evolution, and operation manageability.