Our understanding of the control of cytokinesis is limited in comparison with our knowledge of the controls over the initiation of S phase or mitosis. Study of genetically tractable systems such as Schizosaccharomyces pombe are a useful way to address this problem, since mutants defective in regulation of cytokinesis have been identified. Cloning and analysis of the proteins they encode has begun to shed light upon how formation of the division septum is initiated and directed to the correct place in the cell. Some of these mutants may also be implicated in coordinating mitosis and cytokinesis.