Although rhythmic leaf movement in a higher plant was the first physiological process recognised to be under circadian control, our understanding of the molecular drives underlying circadian rhythms in plants is still limited. Genetic screens for mutants impaired with regard to circadian rhythmicity have identified components critical for clock function in the model plant Arabidopsis thaliana , providing a snapshot of interconnected transcription-based feedback circuits at the core of the clockwork. Subsequently, the Arabidopsis genome project provided the basis for reverse genetic approaches to uncover additional gene products operating close to the core clockwork. We will review recent progress in the dissection of the molecular mechanisms within the basic oscillator and in the incorporation of additional components into the basic clock model.