Liquefaction and related phenomena have been responsible for tremendous amounts of damage in historical earthquake around the world. Especially, its devastating effects sprang to the attention of geotechnical engineers in a three-month period in 1964 when the Niigata earthquake in Japan followed the Good Friday earthquake in Alaska. Evaluation of liquefaction resistance of soils is an important step in many geotechnical investigations in earthquake-liable region. The most common procedure around the world for evaluating liquefaction resistance is ?simplified procedure? developed originally by Seed and Idriss (1971) using blow counts from the Standard Penetration Test correlated with a parameter called the cyclic stress ratio, which represents the cyclic loading on the soil. Since 1971, this procedure has been modified and updated. Parallel procedures based on Cone Penetration Test, Shear wave velocity measurements, and Becker Penetration Test was introduced and has been revised and updated. The simplified procedures are based on empirical considerations and have provided useful methods for identifying liquefaction potentials of soils. However, there has been a growing recognition that elementary consideration of the mechanism of liquefaction can provide improved characterization for liquefaction. The energy approach is considered to be one such mechanistic procedure.