Volcanic-ash clouds are a known hazard to aviation, requiring that aircraft be warned away from ash-contaminated airspace. The exposure of aviation to potential hazards from volcanoes in the United States is significant. In support of existing interagency operations to detect and track volcanic-ash clouds, the United States has prepared a National Volcanic Ash Operations Plan for Aviation to strengthen the warning process in its airspace. The US National Plan documents the responsibilities, communication protocols, and prescribed hazard messages of the Federal Aviation Administration, National Oceanic and Atmospheric Administration, US Geological Survey, and Air Force Weather Agency. The plan introduces a new message format, a Volcano Observatory Notice for Aviation, to provide clear, concise information about volcanic activity, including precursory unrest, to air-traffic controllers (for use in Notices to Airmen) and other aviation users. The plan is online at http://www.ofcm.gov/p35-nvaopa/pdf/FCM-P35-2007-NVAOPA.pdf. While the plan provides general operational practices, it remains the responsibility of the federal agencies involved to implement the described procedures through orders, directives, etc. Since the plan mirrors global guidelines of the International Civil Aviation Organization, it also provides an example that could be adapted by other countries.