The current practice of fish processing generates increasing quantities of side streams and waste, such as skin, heads, frames, viscera, and fillet cut offs. These may account for up to 70% of the fish used in industrial processing. Low-value fish catches, and under-utilized fish species comprise another source of side streams. These side streams have been discarded in the environment leading to environmental problems or they have ended up as low commercial value products, such as feed for fur animals and aquaculture. However, several studies have shown that fish side streams contain valuable bioactive ingredients and fractions, such as fish oils, proteins and peptides, collagen, gelatin, enzymes, chitin, and minerals. These compounds and fractions may provide the opportunity to develop novel applications in health promoting foods, special feeds, nutraceuticals, pharmaceuticals, and cosmetic products. Better utilization of side streams and low-value fish would simultaneously improve both the environmental and ecological sustainability of production. This review summarizes the current knowledge on fish and fish side streams as sources of high-value components such as peptides with antimicrobial, antioxidative, antihypertensive, and antihyperglycemic properties, proteins such as fish collagen and gelatin, fish enzymes, fish oils and fatty acids, polysaccharides like glucosaminoglycans, chitin and chitosan, vitamin D, and minerals. Production technologies for recovering the high-value fractions and potential product applications are discussed. Furthermore, safety aspects related to the raw material, technologies, and fractions are considered.