The identification of cell cycle control and signal transduction components on the centrosome has fostered the idea that the centrosome is more than a microtubule-organizing center. Indeed, recent molecular evidence suggests that the centrosome plays an active role not only in the regulation of microtubule nucleation activity, but also in the coordination of centrosome duplication with cell cycle progression, in stress response and in cell cycle checkpoint control. To achieve these roles, it interacts with a multitude of signal transduction molecules. The specificity of the interactions is mediated through anchoring proteins that bring centrosomal components and regulatory proteins into close proximity. The molecular composition and organization of the centrosome thus reflects its multiple functions.