ISR may refer to:
- Publications
- Information Systems Research, an academic journal in the information systems discipline
- International Socialist Review (disambiguation), any of several U.S. publications
- International Statistical Review, a journal of the International Statistical Institute
- Science
- Incoherent scatter radar, a ground-based technique for studying the ionosphere
- Intersecting Storage Rings, a particle collider at CERN
- Initial State Radiation, in particle physics
- Computers
- Interrupt handler or interrupt service routine, a software routine that is executed in response to an interrupt
- In-Service Register or Interrupt Service Register, a type of register in a Programmable Interrupt Controller used to indicate which interrupts are in progress
- Integrated Service Router, a series of Cisco routers
- Countries
- Italian Social Republic, a client state of Nazi Germany
- ISR, country code for Israel, a Middle Eastern country
- Military
- Intelligence, Surveillance and Reconnaissance (disambiguation), i.e., Joint Functional Component Command for Intelligence, Surveillance and Reconnaissance (JFCC ISR), a subordinate command of the United States Strategic Command
- ISR, for Intelligence, Surveillance, and Reconnaissance, in a military context. See ISTAR
- The US Army Installation Status Report Program
- Other uses
- Injection site reaction, a (usually adverse) reaction to an injection/shot such as erythema, ecchymosis (bruise), inflammation and pain
- International Star Registry
- In-situ recovery, a mining technique involving the direct extraction of mineral rich fluids through boreholes drilled into a deposit.
- Institutional and Scientific Relations Directorate of the European Union
- International Socialist Resistance
- Israir, an Israeli airline
- Institute for Strategy and Reconciliation, an independent, non-profit think tank and international relief and development organization headquartered in Washington DC
- Institute for Social Research - CSUS, a research institution affiliated with California State University, Sacramento
- ISR, or In-Stent Restenosis, renewed blockage of a blood vessel after a stent has been implanted
- International Search Report, an element of patent law. See Patent Cooperation Treaty
- ISR, or Internal Sales Representative, used in business