For over a century, the terms centromere and kinetochore have been used interchangeably to describe a complex locus on eukaryotic chromosomes that attaches chromosomes to spindle fibres and facilitates chromosome movement in mitosis and meiosis. This region has become the focus of research aimed at defining the mechanism of chromosome segregation. A variety of new molecular probes and vastly improved optical-imaging technology have provided much new information on the structure of this locus and raised new hopes that an understanding of its function may soon be at hand.