Structured single-stranded nucleic acids, or aptamers, bind target molecules with high affinity and specificity, which translates into unique therapeutic possibilities. Currently, aptamers can be identified to most proteins, including blood-clotting factors, cell-surface receptors, and transcription factors. Chemical modifications to the oligonucleotides enhance their pharmacokinetics and pharmacodynamics, thus extending their therapeutic potential. Several aptamers have entered the clinical pipeline for applications and diseases such as macular degeneration, coronary artery bypass graft surgery, and various types of cancer. Furthermore, the functional repertoire of aptamers has expanded with the descriptions of multivalent agonistic aptamers and aptamers-siRNA chimeras. This review highlights those aptamers and aptamer-based approaches with particular likelihood of achieving therapeutic application.