Abstract: Traditionally, amino acids are classified as essential amino acids and non-essential amino acids based on their ability of syntheses from metabolic intermediates. Currently, many scientists gave a new concept of functional amino acids, which are defined as those amino acids that participate in and regulate key metabolic pathways and immune systems. These amino acids not only provide blocks for protein synthesis, but also as substrates for many functional compounds. It has been reported that these amino acids can improve health, survival, growth, development, and reproduction of organisms. Crustaceans (e.g., shrimp and crabs) are the second largest aquaculture species worldwide, their feed development play a vital role in industry development. Functional amino acids hold great promise in prevention and treatment of metabolic diseases, intrauterine growth restriction, and infectious diseases (including viral infections). However, there are still some technical difficulties and challenges in the use of crystalline amino acids for research and practical production. At present, the knowledge about amino acid metabolism and functions in crustaceans is still limited, and much of them are based on studies of mammals and fish species. This article highlights current knowledge about the functions of amino acids on molt, adaptation of stress, immune, and antioxidant responses, spawning and larval development of crustaceans. It will help to advance the field of protein nutrition and guide the development of future crustacean feeds.