The book reviews the latest data on all of the different biochemical steps that comprise base excision repair (BER), the primary pathway for removal of alkylation, hydrolytic and oxidative damage to DNA. This monograph covers various aspects from excision of damaged or mismatched bases and repair of baseless sites, through a discussion of the DNA polymerases needed for BER, and eventually to the enzymes that complete the BER process. Where appropriate, the cytotoxic and mutagenic consequences of a failure to complete any particular step in the process are outlined.