The spindle pole body (SPB) serves as the centrosome in yeasts and in a variety of other lower eukaryotes. In Saccharomyces cerevisiae, this organelle controls the assembly of all microtubules in the cell, acting not only as a pole of the mitotic or meiotic spindle but also as the site from which cytoplasmic microtubules emanate. The distinctive structure of the SPB has permitted definition of discrete stages in its duplication and behavior at all stages of the yeast life cycle. In association with genetic analyses, studies of the yeast SPB are providing insights into the mechanisms that control centrosomal behavior in this model eukaryote.