Written by a seasoned geotechnical engineer, this book, a winner of the Japanese Geotechnical Society 2016 publication award, presents a simple and unified approach to modeling various features of geomaterials in general stress systems. It not only covers recent methods and models but also uses real test data to prove their reliability. The author first explains the ideas and formulations for modeling soil features in one-dimensional conditions and then extends the one-dimensional models to three-dimensional ones using the tij concept. He also illustrates the numerical simulations of typical geotechnical problems and the corresponding model tests.