This book provides an elementary introduction to the behavior of solids, at temperatures ranging down from room temperature. it is directed at the level of the second or third year undergraduate student in science and engineering, and provides a concise account of some of the more important properties of the solid state. A strict mathematical approach is avoided, and discussion is limited to qualitative, order of magnitude, explanations of low temperature behavior. The reader is assumed to have an elementary acquaintance with vectors, and with the principles of thermodynamics. References are given at the end, for further reading.