DNA repair pathways usually maintain the integrity of the genome, thereby reducing the onset of cancer, disease and aging phenotypes. Conversely, the requirement for DNA repair and genome maintenance in response to radiation and genotoxic chemotherapeutics, implicates DNA repair proteins as prime targets for improving responses to currently employed anti-cancer regimens. Further, cancer-specific DNA repair defects offer novel approaches for tumor selective therapy. There are over 150 human proteins with functional roles in DNA repair. These fall into 14 general categories, including the classical DNA Repair pathways of Base Excision Repair (BER), Direct Reversal of Damage, Mismatch Excision Repair (MMR), Nucleotide Excision Repair (NER), Homologous Recombination (HR), Non-Homologous End-Joining (NHEJ) and the Fanconi Anemia/DNA crosslink repair pathway, plus proteins that modulate nucleotide pools, DNA polymerases, editing and processing nucleases.