Military aircraft insignia are insignia applied to military aircraft to visually identify the nation or branch of military service to which the aircraft belong. Many insignia are in the form of a circular roundel or modified roundel; other shapes such as stars, crosses, squares, or triangles are also used. Insignia are often displayed on the sides of the fuselage, the upper and lower surfaces of the wings, as well as on the fin or rudder of an aircraft, although considerable variation can be found amongst different air arms and within specific air arms over time.

The first use of national insignia on military aircraft was before the First World War by the French Aéronautique Militaire, which mandated the application of roundels in 1912. The chosen design was the French national cockade, which consisted of a blue-white-red emblem, going outwards from centre to rim, mirroring the colours of the French flag. In addition, aircraft rudders were painted the same colours in vertical stripes, with the blue vertical stripe of the tricolours forwardmost. Similar national cockades were designed and adopted for use as aircraft roundels by the air forces of other countries, including the Royal Flying Corps (RFC) and U.S. Army Air Service.

Of all the early operators of military aircraft, Germany was unusual in not using circular roundels. After evaluating several possible markings, including a black, red, and white checkerboard, a similarly coloured roundel, and black stripes, it chose a black 'iron cross' on a square white field, as it was already in use on various flags, and reflected Germany's heritage as the Holy Roman Empire. The Imperial German Army's mobilisation led to orders in September 1914 to paint all-black Eisernes Kreuz (iron cross) insignia with wide-flared arms over a white field; usually square in shape, on the wings and tails of all aircraft flown by its air arm, then known as the Fliegertruppe des Deutschen Kaiserreiches. The fuselage was also usually marked with a cross on each side, but this was optional. The form and location of the initial cross was largely up to the painter, which led to considerable variation, and even to the white portion being omitted. An iron cross with explicit proportions superseded the first cross in July 1916. Initially, this second cross was also painted on a white field, but in October 1916, it was reduced to a 5 centimetres (2.0 inches) border completely surrounding the cross, even the ends of the flared arms. That same month, the Army's air arm was renamed Deutsche Luftstreitkräfte. In March 1918, a straight black cross with narrow white borders on all sides of the cross was ordered, but proportions were not set until April 1918, resulting in many of those repainted in the field having non-standard proportions. This was then replaced in May by a narrower, straight-armed cross that extended the full chord of wings, with the white border restricted to the sides of the cross's bars. In June, it ceased to be used full chord, with the bars all being the same length. The white on any of these could be omitted when used on a white background, and sometimes on the rudder or on night bombers.

Much like the French roundel, variations of the cross would be used on countries allied with Germany, including the Austro-Hungary (combined with red-white-red stripes on the wings until 1916), Bulgaria, Croatia (stylised as a leaf), Hungary (reversed colours), Romania (a blue-rimmed yellow cross with the tricolour roundel in the middle; the shape was also the stylised monogram of the monarch), and Slovakia (blue cross with a red dot in the middle).

With the dissolution of the German Army's Luftstreitkräfte in May 1920, military insignia would disappear until the rise of the Nazi Party, which imposed new rules on aircraft in 1937, starting with the use of the German red / white / black flag on the tails' starboard side of all aircraft, with the port side showing a Nazi Party flag. When the Luftwaffe's re-establishment was made official, these markings were used by military aircraft, while the 1918 Balkenkreuz crosses were reintroduced. Two standardised proportions of the crosses were introduced by July 1939, with differing widths for the quartet of white 'flanks' on each insignia. When camouflage was introduced prior to the invasion of Poland, the flags were dispensed with, replacing them with a black and white swastika on both sides of the tail. During the ensuing war, the crosses would be further simplified, leaving only the borders in a contrasting colour.

After the Second World War, West Germany reverted to using a variation of the 1916 iron cross, using the white 'flanks' of the Balkenkreuz following the now-curved sides of each arm, while East Germany used a diamond marking based on their flag, with the coat of arms from the flag. The reunification of Germany in 1990 resulted in the West German iron cross replacing the East German insignia for all German military aircraft.

The British Royal Flying Corps (RFC) abandoned their original painted Union Flags because, from a distance, they looked too much like the Eisernes Kreuz (Iron Cross) used on German aircraft. The Royal Naval Air Service (RNAS) used either a plain red ring (with the clear-doped linen covering forming the light coloured centre), or a red-rimmed white circle on their wings for a short period; almost exactly resembling those in simultaneous use by the neutral predecessors of today's Royal Danish Air Force, before both British air arms adopted a roundel resembling the French one, but with the colours reversed, (red-white-blue from centre to rim). The two separate army and naval air arms joined on 1 April 1918 to form the Royal Air Force (RAF).

The British roundel design, with variations in proportions and shades, has existed in one form or another to this very day. The Royal Canadian Air Force (RCAF) roundel was based on the RAF roundel used previously on Canadian military aircraft. From World War I onwards, a variant of the British red-white-blue roundel with the white omitted has been used on camouflaged aircraft, which between the wars meant night bombers. During the Second World War, the colours were toned down and the proportions adjusted to reduce the brightness of the roundel, with the white being reduced to a thin line, or eliminated. In the Asia-Pacific region, the red inner circle of roundels was painted white or light blue to avoid confusion with Hinomaru markings on Japanese aircraft (still used by the Japan Self-Defense Forces to this day), much as the United States roundel omitted the red for the same reason.