Mitosis is the process by which a eukaryotic cell divides to produce two daughter cells that each contain the same number of chromosomes as the parent cell. As this definition suggests, the overall process of mitosis fails if the parent cell's chromosomes don't reach their correct destinations. One structure that plays a critical role in ensuring that this does not occur is the centromere. The centromere was first described by German biologist Walter Flemming in the 1880s as the "primary constriction" of the chromosome. Scientists now appreciate that the centromere is a region of specialized chromatin found within each constricted chromosome that provides the foundation for kinetochore assembly and serves as a site for sister chromatid attachment (Figure 1). Errors in centromere or kinetochore function are catastrophic for cells. Such errors can lead to aberrant division and chromosomal instability, both of which are often observed in cancerous cells.