A squadron in an air force, or naval or army aviation service, is a unit comprising a number of military aircraft and their aircrews, usually of the same type, typically with 12 to 24 aircraft, sometimes divided into three or four flights, depending on aircraft type and air force.

In most armed forces, two or more squadrons will form a group or a wing. Some military forces (including the United States Air Force, United States Space Force, French Air and Space Force, Royal Air Force, German Air Force, Royal Netherlands Air Force, Belgian Air Component and Republic of Singapore Air Force) also use the term "squadron" for non-flying ground units (e.g. radar squadrons, missile squadrons, air defense squadrons, aircraft maintenance squadrons, security forces squadrons, civil engineering squadrons, range operations squadrons, range management squadrons, weather squadrons, medical squadrons, etc.).

In World War I, the Imperial German Army used the term Squadron (staffel), whereas the Austro-Hungarian armed forces and the Swiss Army used the term company. In the modern German Air Force, a flying staffel is a battalion-equivalent, while a ground based support staffel is a company-equivalent. One such example are the air base defence units, which are squadrons (German, plural: Staffeln) formed into battalions. The ground based missile air defence units are also company- (in this case battery-)equivalent squadrons (staffeln).

The Swedish Air Force adopted naval-like traditions in its formative years and for that historical reason calls its squadrons divisions (plural: divisioner). They are grouped into air flotillas (plural: flygflottiljer). During the Cold War the Swedish Army, Navy and Air Force each had their own integral helicopter arms. After the end of it in line with the mid-90s force reduction and reforms they were fused into the Swedish Armed Forces Helicopter Wing as a service, independent from the three main armed forces branches. The Helicopter Wing adopted the term skvadron from the former Swedish Army Aviation for its units, which is squadron in its army company-equivalent meaning. In the early 2000s, the Swedish Air Force absorbed the Helicopter Wing as its fourth combat air wing. Unlike the US Air Force, where the name of the base and the units stationed at that base are not related to each other, the name of the wing (flotilla) is in general considered synonymous with the air base where the unit is stationed. For example, the air base where the F 10 wing is stationed (in Ängelholm) is commonly referred to as F 10 even though it is the name of the tactical unit. In general, this only applies as long as a wing is stationed at the base. Case in point is Uppsala-Ärna air base, an active military airport but since the tactical unit located there has been disbanded it is no longer referred to as F 16. These naming conventions have been inherited from the navy where Swedish military aviation has its roots.

During the infant years of combat aviation in World War I and specifically with the trench stalemate at the front military aircraft partially took over the reconnaissance role from the cavalry. With that in mind the British Royal Flying Corps adopted the squadron nomenclature. After the fusion of the Royal Flying Corps and the Royal Naval Air Service into an independent Royal Air Force, the new armed forces branch introduced its own system of ranks, with the commanders of squadrons becoming squadron leaders.

The rapid sophistication in technology and combat tactics has led to increased requirements and qualifications of the officers in command positions and the commanders of RAF flying squadrons were upgraded in the post-World War II period from squadron leaders to wing commanders. Today RAF flying squadrons are battalion-equivalents, while combat and combat service support ground squadrons such as communications or administrative squadrons are company-equivalents and still usually commanded by squadron leaders.

During the Second World War, a British fighter squadron was a fighting strength of 12 aircraft; this was achieved with about 16 aircraft and 20 pilots assigned to each squadron so the full force could be flown at any time. The squadron was subdivided into two flights - A and B, and then into sections of two or three aircraft - Red and Yellow, Blue and Green - for operations.

Flying units in the Fleet Air Arm and Army Air Corps are also called squadrons. In the latter they are company-equivalent units, divided into flights and grouped into regiments.