Following a change in the mean light level of the visual scene, the sensitivity and kinetics of the retinal response are altered substantially. This well-known process of light adaptation serves to match the limited dynamic range of the neural circuitry to the prevailing range of light intensities in the environment. We hypothesize that the retina more generally adapts its processing strategy to the statistical structure of the visual environment. Here we show that retinal adaptation is also triggered by a change in the second-order statistics of the scene, such as the temporal contrast or the spatial correlation function, at constant mean intensity. This retinal contrast adaptation occurs on a time scale of tens of seconds, during which neuronal firing rates increase or decrease several-fold and the visual message carried by each action potential changes substantially. At least two sites within the retina, with different receptive fields, are involved in controlling this process. The phenomenon shares several characteristics with contrast adaptation observed in cortical neurons and in human psychophysics.