Field and laboratory experiments show that endogenous circatidal rhythms in coastal animals are entrained by exposure to real or simulated tidal cycles of hydrostatic pressure, temperature, salinity, wave agitation, immersion and light. Short pulses (2–3 h) of simulated high tide induce slight phase advances or delays in the free‐running circatidal rhythm of groups of experimental animals, depending upon the time of application. Phase‐response curves derived in this way are less clear‐cut than for typical circadian rhythms, but their pattern suggests that tidally rhythmic behaviour is controlled by truly circatidal (and not circadian) oscillators. The underlying circatidal oscillators appear, in general, to be fairly stable, suggesting that populations of coastal animals are relatively unsusceptible to irregularly timed environmental stimuli associated, say, with severe