Salinity is an ecological key factor in the life of estuarine and coastal plankton, and hence, also in the biology of meroplanktonic decapod crustacean larvae. Its influence has been documented in all principal aspects of larval biology including survival, development, morphology, the moulting cycle, growth, feeding, metabolism, energy partitioning, and behaviour. In this review, detrimental effects of osmotic stress on decapod larvae are exemplified, and interactions with other environmental variables such as temperature or toxic pollutants, or with intrinsic phenomena such as the moulting cycle are shown. Putative relationships between osmoregulatory patterns and the metabolic response to salinity variation are proposed.