Proteomics is a technology platform that is gaining widespread use in drug discovery and drug development programs. Defined as the protein complement of the genome, the proteome is a varied and dynamic repertoire of molecules that in many ways dictates the functional form that is taken by the genome. The importance of proteomics is a direct consequence of the central role that proteins play in establishing the biological phenotype of organisms in healthy and diseased states. Moreover, proteins constitute the vast majority of drug targets against which pharmaceutical drug design processes are initiated. By studying interrelationships between proteins that occur in health and disease and following drug treatment, proteomics contributes important insight that can be used to determine the pathophysiological basis for disease and to study the mechanistic basis for drug action and toxicity. Proteomics is also an effective means to identify biomarkers that have the potential to improve decision making surrounding drug efficacy and safety issues based on data derived from the study of key tissues and the discovery and appropriate utilization of biomarkers.