Aptamers, simply described as chemical antibodies, are synthetic oligonucleotide ligands or peptides that can be isolated in vitro against diverse targets including toxins, bacterial and viral proteins, virus-infected cells, cancer cells and whole pathogenic microorganisms. Aptamers assume a defined three-dimensional structure and generally bind functional sites on their respective targets. They possess the molecular recognition properties of monoclonal antibodies in terms of their high affinity and specificity. The applications of aptamers range from diagnostics and biosensing, target validation, targeted drug delivery, therapeutics, templates for rational drug design to biochemical screening of small molecule leads compounds. This review describes recent progress made in the application of biomedically relevant aptamers and relates them to their future clinical prospects.