This document is intended to augment formal lectures on the general topic of the physical metallurgy of steels, presented within the MSE Department during the Fall Quarter, 1998. It is based on a variety of texts and published articles and also on personal experience. Specific references to sources are made within the document. However, the material is often in the form of knowledge that has been accumulated by the work of many people and is "well-known" by experts in the field. A detailed acknowledgment of the work of each contributor to the field is not attempted because that would be an awesome task. This document is not intended for publication and is restricted for use in MSE 651.01.