Small molecules targeting Aurora A kinase have entered Phase I/II clinical trials. This article shows for the first time that inhibition of Aurora A kinase, using the small molecule inhibitor MLN8054, results in senescence both in vitro and in vivo. Senescent cells are characterized by a large, flat cellular morphology. Shown on the cover are senescent HCT-116 xenograft tumor cells from a mouse treated with MLN8054 [blue DNA stain (DAPI ) and green tubulin stain (cytoplasm)]. For further details and information on additional senescence markers, please see the article by Huck and coworkers on page 373 in this issue.