The following are lists of World War I flying aces. Historically, a flying ace was defined as a military aviator credited with shooting down five or more enemy aircraft during aerial combat. The term was first used by French newspapers, describing Adolphe Pégoud as l'as (the ace), after he downed seven German aircraft.
The notion of an aerial "victory" arose from the first aerial combats, which occurred during the early days of World War I. Unsurprisingly, different air services developed their own definitions of exactly what an aerial victory might be, as well as different methods of assessing and assigning credit for aerial victories.
Ownership of the terrain below had its effect on verifying victory. An enemy aircraft that crashed in enemy held territory obviously could not be verified by the victor's ground troops. Because aerial combat commonly took place over or behind the German lines, German scores are generally considered more accurate because German aces' victories were more easily confirmed on the ground. Additionally, the British handicap of returning home against prevailing wind on the Western Front fattened German scores.
The scores presented in the lists cannot be definitive, but are based on itemized lists that are the best available sources of information. Loss of records by mischance and the passage of time complicates reconstructing the actual count for given aces.
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.