The cytoplasmic level of a messenger RNA, and hence protein, depends not only upon its rates of synthesis, processing, and transport, but its decay rate as well. mRNA decay rates are frequently not static, but vary in response to extracellular stimuli and viral infections. Sequence elements within an mRNA, together with the protein and/or small noncoding RNA factors that bind these elements, dictate its decay rate. Not surprisingly, genetic alterations in mRNA stability can lead to various diseases, including cancer, heart disease, and immune disorders. However, we now have the capacity to alter selective aspects of the mRNA decay machinery by design in order to tune expression of any given gene to desired levels as a means of achieving therapeutic results. Our intent in this review is to introduce the reader to the intricacies of regulated gene expression at the level of mRNA stability, describe the roles of mRNA stability in pathology and drug development, and discuss some recent developments in the field of computational biology that are providing novel tools for understanding specific protein-RNA interactions, which drive the mRNA degradation machinery.