In the 1980s, NATO countries signed a Memorandum of Agreement that the United States would develop a medium-range air-to-air missile to replace the AIM-7 Sparrow, while Britain and Germany would develop a short-range air-to-air missile to replace the AIM-9 Sidewinder. The US design developed as the AIM-120 AMRAAM, while the UK-German design developed as the AIM-132 ASRAAM.
The roots of the ASRAAM dated back to 1968 when development began on the Hawker Siddeley SRAAM ('Taildog'), but this project ended in 1974 with no production orders. This work was dusted off for the UK/German effort, with the Germans providing a new seeker, and the British providing most of the remaining components. In the intervening time, the need for high maneuverability was downgraded in favor of greater range.
After German reunification in 1990, Germany found itself with large stockpiles of the Soviet Vympel R-73 missiles (NATO reporting name: AA-11 Archer) carried by the MiG-29 Fulcrum and concluded that the AA-11's capabilities had been noticeably underestimated. In particular, it was found to be both far more maneuverable, and far more capable in terms of seeker acquisition and tracking than the latest AIM-9 Sidewinder. In 1990 Germany withdrew from the ASRAAM project, while Britain resolved to find another seeker and develop ASRAAM according to the original requirements.
In late 1990, the US partnership expressed similar concerns and embarked on an upgrade to the existing Sidewinder design to provide increased maneuverability and IRCCM (infrared counter counter measures) performance, i.e. measures to counter infrared countermeasures (IRCM). This program was designated AIM-9X.