This article is the first of a multi-part series on traumatic brain injury (TBI). Historically, TBI has received very limited national public policy attention and support. However since it has become the signature injury of the military conflicts in Iraq and Afghanistan, TBI has gained the attention of elected officials, military leaders, policymakers, and the public. This series is being published by the Traumatic Brain Injury-Resource Optimization Center (TBI-ROC) and its Advisory Group, which is facilitated by JBS International, Inc. The TBI-ROC aims to be a recognized source and leader for advancing national attention to the myriad of policy, research, practice, and service needs supporting both civilian and military individuals who incur TBI and their families. In this article, the authors provide a definition of TBI and describe its causes and symptoms.