All living organisms must contend with the consequences of damage to their genetic material, DNA, that is induced by a variety of agents. Exogenous agents include X-rays, ultraviolet light, and a wide variety of chemicals, including many found in cigarette smoke. Endogenous agents include certain chemicals produced during normal metabolism, whereas other DNA aberrations can be introduced by mistakes during DNA replication. At a cellular level, a failure to deal adequately with such DNA damage can result in cell death or mutation, while at an organismic level, it can result in an increased incidence of cancer, accelerated aging, immune system disorders, neurological disorders, and a host of other problems. All organisms, from very simple bacteria to humans, have an impressive set of molecular systems that enable them to repair or temporarily tolerate DNA damage. Many of these systems prevent mutations from being induced by accurately repairing the DNA damage, while others introduce mutations as the molecular price of helping the cells tolerate the damage. Most of these DNA repair systems evolved a long time ago, so that critical knowledge about human DNA repair systems has been gained by studying simpler model organisms. This symposium will bridge science and society by showing how basic scientific investigations of the molecular mechanisms of DNA repair are offering crucial insights into cancer and other human diseases and also suggesting new therapeutic approaches.