The concept of replacing live feeds in larval culture is now some 20 years old and stems from the dual aims of attempts to simplify hatchery feeding regimes and investigation of feeding and nutrition in commercially important larvae. Although total replacement of live feeds is routinely accomplished in the laboratory for penaeids, it has been less successful for caridean and other crustacean larvae. In shrimp hatcheries, it is standard practice to use artificial feed, at least as a supplement or co-feed, but complete replacement with the elimination of algal culture units is rare. The development of microparticles as feed for crustaceans, fish, and even bivalves has facilitated research into the criteria controlling larval ingestion, digestion, and energetic requirements and allowed identification of some major nutritional requirements. From energetic studies, it is apparent that the feeding strategy adopted by herbivorous larvae is more efficient than that adopted by carnivorous crustacean larvae. This explains the success achieved with artificial diets for the former and identifies the requirement for easily digestible high-energy diets for the latter. One further original concept, that of supplying medicinal agents via microparticulate feeds, is also now close to reality. That has been demonstrated from recent research into the positive effects of raising the immune response of crustaceans with formalin killed pathogens, beta glucans, or by supplying the nonpathogenic bacteria as probionts.