Over the last century, the domains of air, space, and cyberspace have joined the traditional warfighting domains of land and sea. While the doctrine for land operations is relatively mature, the doctrine for space and cyberspace continue to evolve, often in an unstructured manner. This monograph examines the relationships among these domains and how they apply to U.S. Army and joint warfighting. It concentrates on the central question: How are U.S. military operations in the newest domains of space and cyberspace being integrated with operations in the traditional domain of land? This inquiry is divided into three major sections: • Existing Doctrine: This section presents an overview of the current state of joint and U.S. Army doctrinal development for each of the domains of land, space, and cyberspace. • Operations in Multiple Domains: This section examines the concept of cross-domain synergy and its ability to enhance globally integrated operations. • Future Operations: This section explores probable future operating environments as well as the resulting implications for U.S. Army and joint force development. It includes recommendations for policymakers and senior leaders regarding the future development and integration of space and cyberspace doctrine. Anticipated future trends favor the decreased emphasis on traditional large-scale land operations and increased frequency and intensity of conflict in space and cyberspace, perhaps even where these newer domains may become preeminent for a given operation. The joint staff’s pursuit of achieving cross-domain synergy in planning and operations offers a credible method to face some of the challenges of the future joint force, but this will likely remain an evolutionary vice revolutionary endeavor.