Abstract: Recently there has been an explosion of research into the genetics of caste determination, especially following thediscovery of systems where queen-worker caste determination has a strong genetic influence. In this review we collateand interpret research on genetic caste determination in ants and discuss this research within the historical frameworkof caste determination in the social insects. While early researchers disagreed over the relative importance of rearingenvironment and genes on caste determination, the notion that caste is determined by environment had been largelysupported by both theory and empirical results – until relatively recently. The growing utility of molecular markers, together with breeding studies and other quantitative genetic approaches, has now demonstrated a genetic component tocaste across numerous social insect taxa. The strength of the genetic component varies and may often remain highlyconditional on the environment. In extreme cases, caste is determined almost exclusively by genotype. We review environmental and genetic factors that affect caste determination, summarize recent evidence for weak and strong geneticcaste determination, and discuss the evolution of these systems. Genotypes that produce queen-biased caste ratios areoften described as cheaters, and here we emphasize that the evolutionary dynamics of genetic caste determination involves the coevolution (often antagonistic) of biasing and restorer genes expressed in interacting nestmates. The evolutionary importance of such conflicts over caste fate remains unclear, but in some cases may lead to widespread dependent lineage systems, sperm parasitism, and workerless social parasites.