As sessile, photosynthetic organisms, plants benefit greatly from a circadian clock that adjusts their overall metabolism in anticipation of the highly predictable arrival of sunrise and sunset. Thus, it is not surprising that about one-third of all plant genes show evidence of circadian regulation in their expression patterns (1, 2). However, closer examination of this diurnally regulated transcription shows that it comprises not only the predictable genes involved in photosynthesis, carbon metabolism, and water uptake but numerous genes with known functions in plant defense. Recent studies show that the success of pathogen infections is influenced by the plant circadian clock (3⇓–5). Accumulation of salicylic acid, a key signal for the induction of antimicrobial defenses, peaks at night and may lead to elevated pathogen resistance in the early morning. Cyclical accumulation of herbivore-induced plant metabolites (6), as well as reciprocal effects of plant secondary metabolism on the circadian clock (7), suggests that resistance to insect herbivory also should show diurnal regulation. This hypothesis is confirmed by a study in PNAS (8), which provides a previously undescribed avenue for studying plant-herbivore interactions by demonstrating that plants can benefit from synchrony in the pattern of diurnally regulated defenses and insect feeding behavior.