Existing research provides foundational insights on the challenges to successful security cooperation; however, the global context today differs considerably from that on which much of the literature is based. Though shifts in military technology, the character of war, and the strategic environment typically reflect gradual evolution rather than revolutionary changes, it is essential to examine how to adapt existing evidence for today’s realities. What are the implications of emerging technologies and warfighting domains, evolutions in warfare, global economic and strategic competition, and U.S. national security strategy? Potential questions include: are there features of the cyber, space, or maritime domains, or of artificial intelligence and autonomous systems, that require rethinking existing practices around defense sales, burden sharing, or defense institutional development? Are there novel issues—strategic, technical, legal, or normative—when partners face irregular threats that extend into non-military domains? When do security cooperation activities by competitors threaten U.S. interests, and what are optimal responses?