Welcome to the emerging world of genomics and deoxyribonucleic acid (DNA) microarray technology. This remarkable and innovative technology has revolutionized how researchers determine changes in the expression levels of genes (actually messenger ribonucleic acids (mRNAs)) between two or more samples. This chapter is intended to introduce students and technical scientists to the fundamental concepts and logistics inherent to DNA microarray work, particularly those aspects relevant to conducting DNA microarray research in the laboratory. It also explores fundamental aspects critical to successfully utilizing microarray technology in the laboratory including (a) the role of DNA hybridizations in microarray technology, (b) the processes and logistics of creating a DNA microarray, (c) the common methods used to prepare samples for DNA microarray hybridization, (d) the critical components of DNA microarray hybridization and processing, and (e) an introduction to DNA microarray scanning. To begin our trek into this realm, we must brie y review the fundamental concepts of cellular and molecular biology.