Assembly of the mitotic spindle is an interesting example of morphogenesis at the cellular level. The temporal control of this major event involves the periodic activation of the cyclin-cdc2 kinase complex. In this review, I report recent results that have shed some light on the temporal regulation of centrosome duplication, microtubule nucleation and microtubule dynamics. Reorganization of highly dynamic microtubules into a bipolar spindle probably requires kinesin and dynein-like motors and their role is discussed in an hypothetical model that may be applicable to all mitotic spindles.