The present paper summarizes the data available in the literature concerning the genotoxicity of carbon nanotubes（CNTs）, whose potential applications and uses are wide and varied, including CNT-enhanced plastics, electromagnetic interference/radio-frequency （EMI/RFI）shielding, antistatic material, flexible fibers and advanced polymers, medical and health applications, and scanning probe microscopy. All data in this review were previously published in openly available scientific literature. Genotoxicity studies, including in vitro and in vivo assays, are available. In genotoxicity tests of single-walled carbon nanotubes（SWCNTs）, positive results were observed on in vitro comet, cytokinesis-blocked micronucleus（CBMN）, and DNA double-strand break assays, as well as on iin vivo comet, K-ras mutation, mitochondrial DNA damage, and oxidatively damaged DNA assays. As for multi-walled carbon nanotubes（MWCNTs）, positive results were shown in an iin vitro gene mutation assay using Aprt-heterozygous mouse embryonic stem cells, the comet assay, CBMN assay, and DNA double-strand breaks assay, as well as in vivo comet, chromosomal aberration, and micronucleus assays. Negative results were also noted in in vitro bacterial gene mutation, chromosomal aberration, and micronucleus assays for SWCNTs and MWCNTs, and in vitro comet and in vivo micronucleus assays for SWCNTs, and an SCE assay for MWCNTs. This review showed that there were inconsistencies in the results of reports on the genotoxicity of CNTs that make it very difficult to draw firm conclusions. The inconsistency of the results on genotoxicity appears to be due to differences in the test substances including physico-chemical characterizations, test conditions, and endpoints between reports. A battery of standard genotoxicity testing methods covering a wide range of mechanisms is useful to clarify the genotoxicity of CNTs.