Ways, mechanisms, and responses of ontogenetic adaptation of reef-building corals to light are discussed on the basis of original and literature data. The possible ways of photoacclimation of corals within the range of tolerance to light are shown: (1) adaptation to bright light (>70% incident photosynthetic active radiation, PARs), (2) adaptation to moderate shade (50–10% PARs), and (3) adaptation to extremely low light (<5% PARs). In each of the ways, general and specific mechanisms and reactions are involved in photoacclimation of corals. Adaptive changes take place in plant (zooxanthellae) and animal (polyps) components of the symbiotic organism. They involve morphology, physiology, and biochemistry of colonial polyps and their zooxanthellae. During changes of the light regime, some adaptive reactions last several months and others occur within a few days. Some physiological and biochemical alterations occur as early as the next day after the light regime changes. The wide range of light tolerance of corals and a great number of mechanisms and reactions of photoacclimation allowing corals to adapt to bright and low light with minimum losses in their metabolic activity give grounds to classify them as a single ecological group of light- and shade-tolerant organisms.