Permanent translocation heterozygotes are found in 3 families and almost 60 species of flowering plants. At least 9 other species in 5 additional families may also have at least some populations that include permanent translocation heterozygotes. The results obtained by analyzing a single locus model of selection in permanent translocation heterozygotes suggest that selection will result in almost complete fixation on the single most fit genotype present in a population as long as recombination is rare. This may provide an explanation for the apparent ecological success of permanent translocation heterozygotes in some groups of organisms. It is not necessary to postulate that their success is the result of hybrid vigor. The analysis and numerical study of a model for linkage modification in permanent translocation heterozygotes indicates that there is selection for reduced recombination, although there are cases in which a neutral allele that increases the linkage of alleles at a selected locus to one chromosome set or the other does not increase when rare. A variety of experimental evidence suggests that the population structure of permanent translocation heterozygotes is quite similar to what is predicted from the single locus selection model. Although many have apparently originated through hybridization of ancestors with different chromosome end arrangements, permanent translocation heterozygotes are not necessarily more genetically heterozygous than pair-forming congeners. Permanent translocation heterozygotes, although they are mostly annuals, biennials, or short-lived perennials and often self-fertilizing, are not necessarily weedier than their close relatives, as is often supposed.