ISF may stand for:

Science and technology

• Incremental sheet forming
• Information Security Forum, an international information security best practices organization
• Ingenieurs Sans Frontieres (Engineers Without Borders)
• Ink Serialized Format, a vector image file format from Microsoft
• Interstitial fluid
• Imaging Science Foundation
• Impulse sensitivity function
• Israel Science Foundation

Education

• Idries Shah Foundation, educational charity
• Independent Schools Foundation Academy, private international school in Hong Kong
• Insaf Student Federation, it is the largest Center-Left Student organization in the Nation and the official student wing of the Pakistan Tehreek-e-Insaf political party
• International School of Florence
• International School Sport Federation, sports governing body for high school sport
• Internationale Schule Frankfurt Rhein-Main

Sport

• International Snowboard Federation
• International Softball Federation
• International Skyrunning Federation, world sports governing body for skyrunning
• International Socca Federation, governing body of small-sided-football
• International Sumo Federation, governing body for amateur sumo

Other

• Importer Security Filing
• Impôt de Solidarité sur la Fortune, a French wealth tax
• International Seafarers' Federation, former international trade secretariat
• Idaho Shakespeare Festival, theater company
• Île Sans Fil, a community wireless network based in Montreal, Canada
• Internal Security Forces, of Lebanon
• Iraqi security forces
• Lexus IS F
• Italian Strategic Fund