This Account describes work done in these laboratories that has used synthetic, physical organic, and biological chemistry to understand the roles played by the nucleobases, sugars, and phosphates of DNA in the molecular recognition processes central to genetics. The number of nucleobases has been increased from 4 to 12, generating an artificially expanded genetic information system. This system is used today in the clinic to monitor the levels of HIV and hepatitis C viruses in patients, helping to manage patient care. Work with uncharged phosphate replacements suggests that a repeating charge is a universal feature of genetic molecules operating in water and will be found in extraterrestrial life (if it is ever encountered). The use of ribose may reflect prebiotic processes in the presence of borate-containing minerals, which stabilize ribose formed from simple organic precursors. A new field, synthetic biology, is emerging on the basis of these experiments, where chemistry mimics biological processes as complicated as Darwinian evolution.