The resistance of a saturated sand to liquefaction under cyclic loading has been assumed to depend only on the void ratio, effective stress system and intensity of cyclic loading. The effect of strain history on the resistance to liquefaction is investigated here by means of triaxial and simple shear tests. The resistance of a saturated sand to liquefaction as measured in laboratory tests is very much influenced by the previous strain history. Partial liquefaction which occurs at small shear strains greatly increases the resistance to liquefaction in subsequent tests. Cycles of large shear strains, or quasi-static shear strains > 7.5%, reduces the resistance to liquefaction. The increase in resistance to liquefaction created by a very small shear strain may result from the elimination of small local instabilities in the original sand structure. The loss of resistance caused by larger shear strains is thought to be due to either the creation of a uniform metastable structure or the development of a nonuniform structure.