Root-knot nematodes (RKNs) (Meloidogyne spp.) are obligate endoparasites of major worldwide economic importance. They exhibit a wide continuum of variation in their reproductive strategies, ranging from amphimixis to obligatory mitotic parthenogenesis. Molecular phylogenetic studies have highlighted divergence between mitotic and meiotic parthenogenetic RKN species and probable interspecific hybridization as critical steps in their speciation and diversification process. The recent completion of the genomes of two RKNs, Meloidogyne hapla and Meloidogyne incognita, that exhibit striking differences in their mode of reproduction (with and without sex, respectively), their geographic distribution, and their host range has opened the way for deciphering the evolutionary significance of (a)sexual reproduction in these parasites. Accumulating evidence suggests that whole-genome duplication (in M. incognita) and horizontal gene transfers (HGTs) represent major forces that have shaped the genome of current RKN species and may account for the extreme adaptive capacities and parasitic success of these nematodes.