Target discovery, which involves the identification and early validation of disease-modifying targets, is an essential first step in the drug discovery pipeline. Indeed, the drive to determine protein function has been stimulated, both in industry and academia, by the completion of the human genome project. In this article, we critically examine the strategies and methodologies used for both the identification and validation of disease-relevant proteins. In particular, we will examine the likely impact of recent technological advances, including genomics, proteomics, small interfering RNA and mouse knockout models, and conclude by speculating on future trends.