DNA microarray technology has been used for genome-wide gene expression studies that incorporate molecular genetics and computer science analyses on massive levels. The availability of microarrays permit the simultaneous analysis of tens of thousands of genes for the purposes of gene discovery, disease diagnosis, improved drug development, and therapeutics tailored to specific disease processes. In this chapter, we provide an overview on the current state of common microarray technologies and platforms. Since many genes contribute to normal functioning, research efforts are moving from the search for a disease-specific gene to the understanding of the biochemical and molecular functioning of a variety of genes whose disrupted interaction in complicated networks can lead to a disease state. The field of microarrays has evolved over the past decade and is now standardized with a high level of quality control, while providing a relatively inexpensive and reliable alternative to studying various aspects of gene expression.