EFF or eff may refer to:

• Economic Freedom Fighters, a South African communist political party
• Economic Freedom Fund, an American political organization
• Election Fighting Fund, a British suffragist organization supporting the early Labour Party
• Electronic Frontier Foundation, a US-based international digital rights group
• Evergreen Freedom Foundation, an American political think tank

• Eff (duo), a German musical duo
• Eff (programming language), a functional programming language with focus on algebraic effects
• Efficiency (basketball), a statistical benchmark
• Effingham Junction railway station, Surrey, England, National Rail station code
• The Electronic Font Foundry, a British computer type foundry
• Emmett/Furla Films, now Emmett/Furla Oasis Films, an American production company
• Environmental Film Festival in the Nation's Capital, in Washington, D.C., United States
• Ethiopian Football Federation
• Extrusion freeform fabrication, a method for fabricating functionally graded material
• F, a letter of the alphabet
• A minced oath of the obscenity Fuck

• F (disambiguation)