Published data on the structure and mechanism of endonuclease V from bacteriophage T4 are reviewed with the objective of developing a working mechanistic model of this enzyme. Endonuclease V is an interesting and important candidate to be the first DNA-repair enzyme to have its structure determined by crystallography, and a more detailed model of the reaction process is needed to mechanistically interpret such a structure. Such a model should be sufficiently detailed to support future investigations of structure/function relationships between the enzyme and the DNA damage repair pathway it initiates, as probed by site-directed mutagenesis techniques and other methods. The early literature is presented in an historical perspective, followed by a description of prior models and biochemical investigations. The biochemical phenotypes of mutants in the enzyme structural gene are discussed. The results of computer analyses aimed at structural interpretations of the protein sequence are given, together with a brief discussion of the strengths and weaknesses of such experiments.