4F

4F or 4-F may refer to:
 * 4F (company), a Polish sportswear company
 * 4-F classification in the U.S. Selective Service System, identifying a person as unfit for military service
 * 4F correlator, in Fourier optics
 * The 4f electron shell
 * Section 4(f) of the United States DOT act of 1966, which regulates acquiring park and historic properties for transportation use.
 * 4F case, a 4 February 2006 controversial criminal case in Barcelona
 * Flottille 4F a French naval aviation squadron
 * LMS Fowler Class 4F, a class of 0-6-0 steam locomotive
 * February 1992 Venezuelan coup d'état attempt, known in Venezuela as "4F".