World War I was the first major conflict involving the use of aircraft. Tethered observation balloons had already been employed in several wars and would be used extensively for artillery spotting. Germany employed Zeppelins for reconnaissance over the North Sea and Baltic and also for strategic bombing raids over Britain and the Eastern Front.

Airplanes were just coming into military use at the outset of the war. Initially, they were used mostly for reconnaissance. Pilots and engineers learned from experience, leading to the development of many specialized types, including fighters, bombers, and trench strafers.

Ace fighter pilots were portrayed as modern knights, and many became popular heroes. The war also saw the appointment of high-ranking officers to direct the belligerent nations' air war efforts.

While the impact of airplanes on the course of the war was mainly tactical rather than strategic, the most important role being direct cooperation with ground forces (especially ranging and correcting artillery fire), the first steps in the strategic roles of aircraft in future wars were also foreshadowed.

At the 1911 meeting of the Institute of International Law in Madrid, legislation was proposed to limit the use of aeroplanes to reconnaissance missions and banning them from being used as platforms for weapons. This legislation was rooted in a fear that aeroplanes would be used to attack undefended cities, violating Article 25 of the Den Hague Reglement (the set of international laws governing warfare).

At the start of the war, there was some debate over the usefulness of aircraft in warfare. Many senior officers, in particular, remained skeptical. However the initial campaigns of 1914 proved that cavalry could no longer provide the reconnaissance expected by their generals, in the face of the greatly increased firepower of twentieth century armies, and it was quickly realised that aircraft could at least locate the enemy, even if early air reconnaissance was hampered by the newness of the techniques involved. Early skepticism and low expectations quickly turned to unrealistic demands beyond the capabilities of the primitive aircraft available.

Even so, air reconnaissance played a critical role in the "war of movement" of 1914, especially in helping the Allies halt the German invasion of France. Aircraft were first used in Alexander von Kluck's German First Army during the Battle of Mons to target its guns on British II Corps positions. On 22 August 1914, British Captain L.E.O. Charlton and Lieutenant V.H.N. Wadham of the Royal Flying Corps (RFC) reported von Kluck's forces were preparing to surround the British Expeditionary Force, contradicting all other intelligence. The British High Command took note of the report and started to withdraw from Mons, saving the lives of 100,000 soldiers. Later, during the First Battle of the Marne, observation aircraft discovered weak points and exposed flanks in the German lines, allowing the allies to take advantage of them.

In Germany the great successes of the early Zeppelin airships had largely overshadowed the importance of heavier-than-air aircraft. Out of a paper strength of about 230 aircraft belonging to the army in August 1914 only 180 or so were of any use. The French military aviation exercises of 1911, 1912, and 1913 had pioneered cooperation with the cavalry (reconnaissance) and artillery (spotting), but the momentum was, if anything, slacking.