The US Department of Defense (DOD) is evolving to meet new security challenges in the twenty-first century. Today's challenges result from growing political, environmental, and economic instability in important areas of the globe that threaten national and global security. Immediate outreach to foreign nations in times of violent instability or natural disaster fosters security and stability both for the affected country and for the United States. Foreign humanitarian assistance (FHA) is a rapidly evolving military mission that addresses conflict prevention, conflict, postconflict, and natural disasters. With DOD's extensive global medical resources, it is often uniquely qualified to execute a critical role in relief and/or public health efforts. When and how the American military will act in FHA and disaster relief is a still evolving doctrine with three issues deserving particular attention: aligning operations with host government leadership, preserving humanitarian space, and tailoring the US military's unique resources to the specific political and medical situation at hand. The DOD's response to a large-scale earthquake in Peru suggests useful approaches to these three issues, provides a template for future FHA mission, and points to strategic decisions and operational capabilities that need further development to establish the FHA mission firmly within DOD's repertoire of security engagement activities.