We investigated the diversity of a collection of 76 Xenorhabdus strains, isolated from at least 27 species of Steinernema nematodes and collected in 32 countries, using three complementary approaches: 16S rRNA gene sequencing, molecular typing and phenotypic characterization. The 16S rRNA gene sequences of the Xenorhabdus strains were highly conserved (similarity coefficient >95 %), suggesting that the common ancestor of the genus probably emerged between 250 and 500 million years ago. Based on comparisons of the 16S rRNA gene sequences, we identified 13 groups and seven unique sequences. This classification was confirmed by analysis of molecular typing profiles of the strains, leading to the classification of new isolates into the Xenorhabdus species described previously and the description of ten novel Xenorhabdus species: Xenorhabdus cabanillasii sp. nov. (type strain USTX62(T)=CIP 109066(T)=DSM 17905(T)), Xenorhabdus doucetiae sp. nov. (type strain FRM16(T)=CIP 109074(T)=DSM 17909(T)), Xenorhabdus griffiniae sp. nov. (type strain ID10(T)=CIP 109073(T)=DSM 17911(T)), Xenorhabdus hominickii sp. nov. (type strain KE01(T)=CIP 109072(T)=DSM 17903(T)), Xenorhabdus koppenhoeferi sp. nov. (type strain USNJ01(T)=CIP 109199(T)=DSM 18168(T)), Xenorhabdus kozodoii sp. nov. (type strain SaV(T)=CIP 109068(T)=DSM 17907(T)), Xenorhabdus mauleonii sp. nov. (type strain VC01(T)=CIP 109075(T)=DSM 17908(T)), Xenorhabdus miraniensis sp. nov. (type strain Q1(T)=CIP 109069(T)=DSM 17902(T)), Xenorhabdus romanii sp. nov. (type strain PR06-A(T)=CIP 109070(T)=DSM 17910(T)) and Xenorhabdus stockiae sp. nov. (type strain TH01(T)=CIP 109067(T)=DSM 17904(T)). The Xenorhabdus strains studied here had very similar phenotypic patterns, but phenotypic features nonetheless differentiated the following species: X. bovienii, X. cabanillasii, X. hominickii, X. kozodoii, X. nematophila, X. poinarii and X. szentirmaii. Based on phenotypic analysis, we identified two major groups of strains. Phenotypic group G(A) comprised strains able to grow at temperatures of 35-42 degrees C, whereas phenotypic group G(B) comprised strains that grew at temperatures below 35 degrees C, suggesting that some Xenorhabdus species may be adapted to tropical or temperate regions and/or influenced by the growth and development temperature of their nematode host.