Aptamers are oligonucleotides evolved in vitro or in nature to bind target ligands with high affinity and specificity. They are emerging as powerful tools in the fields of therapeutics, drug development, target validation and diagnostics. Aptamers are attractive alternatives to antibody- and small-molecule-based therapeutics owing to their stability, low toxicity, low immunogenicity and improved safety. With the recent approval of the first aptamer drug Macugen by the US FDA, there is great impetus to develop therapeutic aptamers that can target a wide array of disease states. The recent demonstration that aptamer activity can be reversed by the administration of a simple antidote greatly enhances the potential value of aptamers as therapeutic agents.