Our laboratories and research are directed towards understanding the mechanism by which eukaryotic organisms keep time on a daily basis, and how this capacity to keep time is used to regulate metabolism and development. Circadian clocks with fundamentally identical characteristics are found in all groups of eukaryotic organisms, but the uses to which these clock are put reflects the diversity of evolution. Phylogenetically this ranges from the control of cell division and enzyme activities in unicells, to a firmly established involvement in plant and animal photoperiodism and in avian and insect celestial navigation, to multiplicity of human systems including endocrine function, work-rest cycles and sleep, and drug tolerances and effectiveness.