Plant morphogenesis relies on cell proliferation and differentiation strictly controlled in space and time. As in other eukaryotes, progression through the plant cell cycle is governed by cyclin-dependent kinases (CDKs) that associate with their activator proteins called cyclins (CYCs), and the activity of CYC–CDK is modulated at both transcriptional and post-translational levels. Compared with animals and yeasts, plants generally possess many more genes encoding core cell cycle regulators and it has been puzzling how their functions are specified or overlapped in development or in response to various environmental changes. Thanks to the recent advances in high-throughput, genome-wide transcriptome and proteomic technologies, we are finally beginning to see how core regulators are assembled during the cell cycle and how their activities are modified by developmental and environmental cues. In this review we will summarize the latest progress in plant cell cycle research and provide an overview of some of the emerging molecular interfaces that link upstream signaling cascades and cell cycle regulation.