Accurate chromosome segregation constitutes the basis of inheritance. Mistakes in chromosome segregation during mitosis lead to aneuploidy, a common feature of tumors. The accuracy of chromosome segregation is governed by a complex network of processes which ensure that each daughter cell receives the correct number of chromosomes. Herein we review recent developments in the understanding of chromosome segregation, focusing on the cohesion that holds the sister chromatids together and the spindle checkpoint which regulates anaphase onset.