Chromosome segregation is a complex and astonishingly accurate process whose inner
working is beginning to be understood at the molecular level. The spindle checkpoint plays
a key role in ensuring the fidelity of this process. It monitors the interactions between
chromosomes and microtubules, and delays mitotic progression to allow extra time to correct
defects. Here, we review and integrate findings on the dynamics of checkpoint proteins at
kinetochores with structural information about signalling complexes.