Circadian physiology provides a series of phase cues across the solar day, according to which various physiological and developmental processes can be optimally aligned to times that are most adaptive.  It does so by placing the internal biological clock (a 24 hr time-keeping system) in register with local time. While much is know about the molecular clockworks and about mechanisms that promote clock synchrony, much less is known about the neuronal mechanisms  used by circadian pacemakers to generate and then transmit different phase cues to downstream (non-pacemaker) centers.  In this seminar I will describe studies of rhythmic neuronal activity in vivo in Drosophila, focusing first on the pacemaker network, then considering whether such rhythms may be propagated to other parts of the brain, which lack strong endogenous clock properties.