The mission of the United States Air Force is to fly, fight, and win in air, space, and cyberspace. A crucial part of achieving that mission involves obtaining and maintaining superiority in the air domain. That domain, defined for the first time in this publication, is the area, beginning at the Earth's surface, where the atmosphere has a major effect on the movement, maneuver, and employment of joint forces. Within that domain, forces exercise degrees of control or levels of influence, characterized as parity, superiority, or supremacy. The US has enjoyed at least air superiority in all conflicts since the Korean War. The US will probably retain that superiority in today's ongoing conflicts, but the prospect of near-peer competitors in the not-too-distant future raise the possibility of air parity - a condition in the air battle in which one force does not have air superiority over others - or even conceding superiority to the adversary if Air Force forces are not properly employed.