Cells undergo dramatic shape transitions as they progress through the cell cycle. Here, we discuss how communication between the ubiquitous cell cycle regulator Cdk1 and cell morphology factors such as Cdc42 coordinates the cell cycle and cell morphology in the budding and fission yeasts. During interphase, Cdk1 directly controls components of the Cdc42 regulatory module to promote polarized growth and morphological transitions. Cell morphology factors subsequently provide signals to control the Cdk1-dependent processes of mitosis and cytokinesis at the end of the cell cycle. This suggests that bidirectional signaling promotes coordinated morphology changes during the cell cycle, with general mechanisms that might operate more broadly in eukaryotic cells.