In quantum field theory, the GIM mechanism (or Glashow–Iliopoulos–Maiani mechanism) is the mechanism by which flavour-changing neutral currents (FCNCs) are suppressed. It also explains why weak interactions that change strangeness by 2 (ΔS = 2 transitions) are suppressed while those that change strangeness by 1 (ΔS = 1 transitions) are allowed. The mechanism was put forth by Sheldon Lee Glashow, John Iliopoulos and Luciano Maiani in their famous paper "Weak Interactions with Lepton–Hadron Symmetry" published in Physical Review D in 1970.