Learning solid-state physics requires a certain degree of maturity, since it involvestying together diverse concepts from many areas of physics. The objective is tounderstand, in a basic way, how solid materials behave. To do this one needs botha good physical and mathematical background. One definition of .solid-statephysics is that it is the study of the physical （e,g. the electrical, dielectric,magnetic, elastic, and thermal） properties of solids in terms of basic physical laws.In one sense, solid-state physics is more like chemistry than some other branchesof physics because it focuses on common properties of large classes of materials.It is typical that solid-state physics emphasizes how physical properties link to theelectronic structure. In this book we will emphasize crystalline solids （which areperiodic 3D arrays of atoms）.