ISAR or Isar may refer to:

• Intergovernmental Working Group of Experts on International Standards of Accounting and Reporting
• International Search and Rescue Competition
• Institute for the Study of Academic Racism
• Inverse synthetic aperture radar, a technique to generate two-dimensional radar images of a target
• Intelligible semi-automated reasoning, the formal proof language of the Isabelle proof assistant

• Isar, a German river
  • Isar Nuclear Power Plant, on the river
• Isar, Province of Burgos, a municipality located in Castile and León, Spain
• Isar Rural District, Iran
• Isar, Marvinci, North Macedonia, an archaeological site
• Isar Aerospace, a private German launch vehicle company
• Glas Isar, a small car produced by Hans Glas GmbH