The use of molecular biology and biochemistry to study the regulation of gene expression has become a major feature of research in the biological sciences. Many excellent books and reviews exist that examine the experimental methodology employed in specific areas of molecular biology and regulation of gene expression. However, we have noticed a lack of books, especially textbooks, that provide an overview of the rationale and general experimental approaches used to examine chemically or disease-mediated alterations in gene expression in mammalian systems. For example, it has been difficult to find appropriate texts that examine specific experimental goals, such as proving that an increased level of mRNA for a given gene is attributable to an increase in transcription rates. Regulation of Gene Expression: Molecular Mechanisms is intended to serve as either a textbook for graduate students or as a basic reference for laboratory personnel. Indeed, we are using this book to teach a graduate-level class at The Pennsylvania State University. For more details about this class, please visit http: //moltox. cas. psu. edu and select "Courses. " The goal for our work is to provide an overview of the various methods and approaches to characterize possible mechanisms of gene regulation. Further, we have attempted to provide a framework for students to develop an understanding of how to determine the various mechanisms that lead to altered activity of a specific protein within a cell.