The decay of mRNA plays an important role in the regulation of gene expression. Although relatively ignored for many years and regarded as a simple ribonucleotide salvage pathway, mRNA decay has been established in recent years as a well-defined cellular process that plays an integral role in determining gene expression. The recent application of microarray methods to the study of diverse organisms will help us to better understand these gene regulatory circuits and the influence of transcript stability on gene expression. DNA microarray technology is the method of choice to study individual mRNA half-lives on a global scale. It is important to standardize these methods to generate reproducible and reliable results. In this chapter, we describe experimental designs for the analysis of mRNA decay on a genome-wide scale and provide detailed protocols for each experimental step. We also present an analysis of the decay of chromosomally encoded mRNAs in E. coli.