Interservice rivalry is rivalry between different branches of a country's armed forces. This may include competition between land, marine, naval, coastal, air, or space forces.

Interservice rivalry can occur over such topics as the appropriation of the military budget, prestige, or the possession of certain types of equipment or units. The latter case can arise, for example, when a navy operates naval aviation units, which can be viewed by the air force as an infringement of its traditional responsibilities.

For the most part, interservice rivalries may only be limited to administrative or internal functions, and the branches may otherwise have warm relations and a willingness to work together when necessary, with the rivalries usually only manifesting as in-jokes and light-hearted stereotypes (such as, in the United States Armed Forces, the stereotype that marines eat crayons) or, in more serious contexts, organisational politics disputes that are usually resolved over time. However, in rare instances, interservice rivalries may be so severe that the branches will outright refuse to cooperate or may even sabotage each other, even during an ongoing war or when lives are at stake (such as the rivalry between the Imperial Japanese Army and Imperial Japanese Navy).

The term also applies to rivalries between a country’s intelligence services and law enforcement agencies (e.g. the FBI and CIA in the United States), the emergency services of a jurisdiction (e.g. the NYPD and FDNY in New York City) or separate services in the same field (e.g. the LAPD and LASD in Los Angeles County, California).

Many military analysts consider the Wehrmacht, Nazi Germany's armed forces, as the pioneers of "jointness" (German: integrierter Kriegführung), pointing out that blitzkrieg, the war-fighting style that brought the Wehrmacht stunning victories between 1939 and 1941, depended upon the close integration of ground and air (and sometimes naval) forces and that even after the blitzkrieg campaigns gave way to a drawn-out war of attrition, the Wehrmacht routinely conducted operations in a way that would today be called "joint". That is, elements of two or more services participated in close cooperation with mutually agreed goals, relatively little interservice rivalry, and a command structure that, at least at the "sharp end" of operations, promoted, rather than inhibited, a spirit of jointness. Consequently, analysts assert, the Wehrmacht enhanced its capabilities and improved its combat effectiveness.

Adolf Hitler understood the value of integrating his land, sea, and air forces and placing them under a unified command, the Oberkommando der Wehrmacht (first under Field Marshal Werner von Blomberg's command; later his own). He also saw the benefit of placing them under operational commanders who possessed at least a rudimentary understanding of the tactics, techniques, needs, capabilities, and limitations of each of the services functioning in their combat zone. Hitler was thus innovative and several years ahead of his peers in the West, Italy, and the Soviet Union. Yet, largely because of Hitler's unusual and autocratic command style and difficulties with delegation, the Wehrmacht lacked elements that today's theorists consider essential to the attainment of truly productive jointness (a single joint commander or Joint Chief of Staff, a proper joint staff, a joint planning process, and an absence of inter-service rivalry) and that, as a result, it often suffered needless difficulties in combat.

The rivalries shaped between security organisations in Iran are as follows:

Infighting occurred between the Indian Army and Indian Air Force over the use of attack helicopters came to light during the Kargil War in 1999. This dispute erupted again in 2012 when both the two branches fought over the allocation of AH-64D Apache Longbow helicopters.