In this chapter, we discuss general principles of gene structure and expression as well as mechanisms underlying the regulation of tissue-specific and inducible gene expression. We will see that proteins (transcription factors) control gene transcription by interacting with regulatory elements in DNA (e.g., promoters and enhancers). Because many transcription factors are effector molecules in signal-transduction pathways, these transcription factors can coordinately regulate gene expression in response to physiological stimuli. Finally, we describe the important roles of epigenetic and post-transcriptional regulation of gene expression. Because many of the proteins and DNA sequences are known by abbreviations, the Glossary at the end of the chapter identifies these entities.