The term ace (now commonly flying ace) was first used by French newspapers during World War I, describing Adolphe Pégoud as l'as ('the ace'), after he downed five German aircraft. When aircraft began to shoot or force down other aircraft, systems to count "air victories" were subsequently developed. The American qualification of five victories eventually became the standard, even though other air services had previously used differing figures.^[1]

While "ace" status was most often won by fighter pilots, bomber and reconnaissance crews, and observers in two-seater aircraft such as the Bristol F.2b ("Bristol Fighter"), also destroyed enemy aircraft. If a two-seater aircraft destroyed an aircraft, both crew members were credited with a victory. Because pilots usually teamed with differing observer/gunners in two-seater aircraft, an observer might be an ace when his pilot was not, and vice versa.^[2] The few aces among combat aviators have historically accounted for the majority of air-to-air victories in military history.^[3]

Loss of records by mischance and the passage of time complicates reconstructing the actual count for given aces. The scores presented in the list cannot be definitive, but are based on itemized lists that are the best available sources of information.^[4] Aces are listed after verifying the date and location of combat, and the foe vanquished, for every victory accredited by an aviator's home air service using their own aerial victory standards. Those victories for which the evidence is unavailable or fragmentary have been excluded from the victory count.