The first review in this volume, by Anne-Laure Ban˜uls, Mallorie Hide and Franck Prugnolle from l’Institut pour la Recherche et De´veloppement in Montpellier, France, considers the recent advances in knowledge of the genetics of species of the genus Leishmania and examines the ways in which these advances can help in the interpretation of the taxonomy and population structure of the organisms themselves and the epidemiology and pathogenicity of the infections they produce in humans.