This book provides a comprehensive guide to the taxonomy, morphology, biology, and identification of parasitic crustaceans across marine, brackish, and freshwater environments. It presents practical methodologies for studying these organisms, including contemporary approaches such as DNA-based analyses and digital imaging, alongside established taxonomic techniques. The volume examines host-parasite interactions, life-history strategies, reproductive biology, and moulting processes, offering valuable insights into the diversity and ecology of major parasitic crustacean groups. It also covers emerging issues relevant to fisheries and aquaculture, including the effects of climate change, species introductions, and the expansion of global aquaculture systems. Designed as both a reference and teaching resource, the book supports students, researchers, taxonomists, parasitologists, fisheries scientists, and aquaculture professionals by providing an authoritative and up-to-date synthesis of current knowledge. By integrating foundational concepts with recent advances and methodological developments, it delivers a practical framework for the study, identification, and management of parasitic crustaceans and their interactions with aquatic hosts.