Preliminary abstract: Since 2001, two million members of the United States' armed services have been deployed to Afghanistan and Iraq to wage the country's two most recent and protracted wars. Mild traumatic brain injury (mild TBI), also known as concussion, is one of the most common injuries sustained by these troops and it has become known as one of the 'signature wounds' of the two post-9/11 wars. The etiology and the long-term effects of the injury are poorly defined, but mild TBI seems to be an emerging vocabulary the post-combat symptoms that some service members experience, and perhaps for 'invisible' combat injuries more generally. This research addresses how historically-specific conceptions of combat injuries and discourses of disability shape emerging constructions of mild TBI as a combat wound. In a twelve-month ethnographic study situated in the largest integrated healthcare organization in the Department of Veterans Affairs (VA), this research investigates mild TBI as it is constituted in medical research, clinical diagnosis, and the VA's unique disability benefits system, from the perspectives of medical researchers, clinicians, patients, and benefits officers.