The Three Fs were a series of demands issued by Irish nationalists in their campaign for land reform in Ireland. They were

• fair rent
• free sale
• fixity of tenure

Many historians argue that their absence contributed severely to the Great Irish Famine (1846-49), as it allowed the mass eviction of starving tenants. The Three Fs were campaigned for by a number of political movements, notably the Independent Irish Party and later the Irish Parliamentary Party. They were conceded by the British Government in a series of Land Acts enacted from the 1870s on.

In another context, the "three Fs" is also an informal mnemonic used by educators to help psychology students remember the primary triggers for sympathetic nervous system activity: fear, fighting and sexual arousal (fuck).