AbstractThis chapter summarizes the achievements of tomato breeders over the last century and the developments in research. It covers genetic variation within the genus Lycopersicon, diversity among and within wild species of Lycopersicon, collection and preservation of genetic resources, cytogenetics, molecular linkage maps, applications of molecular markers, map-based cloning, history of tomato breeding (breeding for resistance to biotic stress and abiotic factors, for specific production systems, or for quality), seed production, biotechnology, and transgenic or genetically modified organisms.