This chapter describes the diversity of aquatic organisms from micro- and macroalgae, crustaceans, molluscs, and finfish from freshwater and marine systems which are used for food, feed, and other purposes. A large share of these aquatic resources is harvested from natural stocks by capture fishery. But nowadays, more than half of aquatic foods are produced in aquacultures of different intensities. These aquaculture systems differ depending on the requirements of the cultured organisms and on local circumstances. Aquaculture plays an important role in food and nutrition security and is an essential part of (circular) bioeconomy systems as it can be efficiently integrated into flows of nutrients, water, and feed resources.