Soil mechanics is the study of the response of soils to loads. These loads may come from human-made structures (e.g., buildings), gravity (earth pressures), and natural phenomena (e.g., earthquake). Soils are natural, complex materials consisting of solids, liquids, and gases. To study soil behavior, we have a couple of concepts in solid mechanics (e.g., statics) and fluid mechanics. However, these mechanics are insufficient to obtain a complete understanding of soil behavior because of the uncertainties of the applied loads, the vagaries of natural forces, and the intricate, natural distribution of different soil types. We have to utilize these mechanics with simplifying assumptions and call on experience to make decisions (judgment) on soil behavior.