This text is for the junior/senior core course in soil mechanics and foundations for civil engineering students. It presents the basic theories of soil mechanics in a clear, simple and up-to-date way, combining both classical and critical state theories. This is one of the only texts that adopts the critical state approach to soil mechanics at an undergraduate level. The treatment of soil mechanics is essentially theoretical, but is not highly mathematical and soil behavior is represented by relatively simple equations with clearly defined parameters.