Accurate segregation of chromosomes in mitosis requires that spindle microtubules attach sister kinetochores to opposite poles of the mitotic spindle (biorientation). To achieve biorientation of all chromosomes, incorrect attachments are selectively destabilized, providing a fresh opportunity to biorient, whereas correct attachments are stabilized. Tension across the centromere may be the signal that distinguishes different attachment states, as spindle microtubules pull bioriented sister kinetochores in the opposite direction. Destabilization of incorrect attachments requires the Ipl1/Aurora B kinase, which phosphorylates kinetochore substrates that directly interact with microtubules. The present review focuses on how Aurora B regulates attachments in response to centromere tension.