The U.S. Department of Defense (DoD) has invested in the development of technologies that allow the human brain to communicate directly with machines, including the development of implantable neural interfaces able to transfer data between the human brain and the digital world. This technology, known as brain-computer interface (BCI), may eventually be used to monitor a soldier's cognitive workload, control a drone swarm, or link with a prosthetic, among other examples. Further technological advances could support human-machine decisionmaking, human-to-human communication, system control, performance enhancement and monitoring, and training. However, numerous policy, safety, legal, and ethical issues should be evaluated before the technology is widely deployed. With this report, the authors developed a methodology for studying potential applications for emerging technology. This included developing a national security game to explore the use of BCI in combat scenarios; convening experts in military operations, human performance, and neurology to explore how the technology might affect military tactics, which aspects may be most beneficial, and which aspects might present risks; and offering recommendations to policymakers.