The prevailing paradigm proposes that the core clock molecular circuitry functions based on interlocked negative transcription-translation feedback loops, yet the underlying molecular mechanisms are largely unknown. The discovery that circadian oscillations persist in self- sustained cell autonomous manner in cultured cells provides a relatively facile system for the analysis and identification of the oscillator properties. We employ “state of the art” methods to monitor circadian oscillations in living cells for several successive days using arsenal of circadian reporters. These reporters consist of a circadian promoter that drives the expression of luciferase or florescent protein. Using these assays we can test the involvement of any protein/metabolite of interest in the clock’s function.