A three-letter abbreviation, ISR has several meanings. For instance, it could refer to the European Union's Institutional and Scientific Relations Directorate. It could be the International Star Registry. In patent law, ISR could stand for International Search Report. In a military framework it could mean Intelligence, Surveillance and Reconnaissance. In computer science it refers to Interrupt Service Register or In-Service Register. It could also be used to stand for the Intersecting Storage Rings, which is a particle collider located at CERN. ISR could simply stand for Israel. Information, Storage and Retrieval is another full form of the acronym ISR. In particle physics it could be used to mean Initial State Radiation. In the study of the ionosphere it could mean Incoherent scatter Radar. It could refer to the U.S Socialist magazine International Socialist Review. There is also Interrupt Service Routine, which is a software routine executed as a response to an interrupt.