Considerable progress has been achieved in the identification and molecular characterisation of genes and/or cDNAs coding for cyclin-dependent kinases (CDK) as well as cyclins in diverse plant species including Arabidopsis thaliana. Their transcriptional control during the cell cycle progression and the response to developmental cues and environmental signals has been studied in much detail, although the transcription factors mediating this regulation have yet to be identified. Experimental evidence has validated the involvement of CDKs and cyclins in cell division control in Arabidopsis and has revealed differential activation of two Arabidopsis CDKs in the course of the cell cycle. Finally, the first active CDK/cyclin pairs are being characterised, providing the basis for elucidation of their specific functions in cell cycle control and for unravelling the mechanisms that control their activity.