Liquefaction is a kind of ground failure which tends to occur during strong seismic shaking in loose, saturated non-cohesive soils. This chapter discusses the liquefaction triggering mechanism considering a variety of soils in terms of the influencing factors and how to evaluate the liquefaction potential for engineering purposes, followed by post-liquefaction soil behaviors in terms of residual strengths and deformations. It addresses mitigation measures for liquefaction as well as base-isolation effects of earthquake motions in liquefied deposits. In order to understand the essence of liquefaction behavior, two typical test results are used: a scaled model test of saturated sand deposit as a total system and an undrained cyclic loading test on a saturated sand specimen as a soil element from the deposit. The chapter then addresses some test results on decomposed granite to see the effect of particle crushability on the liquefaction resistance in comparison with non-crushable fluvial granular soils of fresh grains.