Genetic and breeding studies in Oreochromis aureus, O. mossambicus; O. niloticus and O. urolepis hornorium are reviewed. The saddleback phenotypes in O. aureus is controlled by a dominant lethal autosomal gene. The stumpbody phenotype in O. aureus is a nonheritable congenital defect. Genetics of sex and body color are not completely understood. Strain differences for pigmentation, cold tolerance, growth, fecundity, and success in reproducing with other species were found for O. niloticus. There have been three selection programs to improve early growth in O. niloticus. Two were successful. The third was successful, realized heritability for weight was 0.19 after three generations of selection. One generation of selection improved growth by 10.7 to 15.5% in O. aureus. One generation of selection improved weight gain in O. mossambicus by 7.0%. Proposals to improve efficiency of selection for growth have included selection, family selection, and weight-specific selection. Crossbreeding between strains of O. niloticus improved growth by as much as 36%. Cold tolerance has been improved by interspecific hybridization, and this trait was transferred from O. aureus to a cold-sensitive population of red tilapia by back-crossing. An inbreeding study in O. mossambicus showed that the inbred group had lower survival and growth rates than crossbred controls. Triploids, tetraploid, and gynogenetic tilapias have been produced by chromosomal manipulation.