Crustaceans are a large group of arthropods with over 67,000 known species that inhabit a wide range of habitats including freshwater, estuarine and sea water. This chapter reviews the main diseases of crustaceans caused bacteria. Many species of bacteria are pathogens of these animals but vibrios are the main group of pathogens. In particular, Vibrio parahaemolyticus strains are major pathogens of shrimp and other crustaceans. Strains of this bacterium that exhibit the production of a binary cytotoxin cause a condition called acute hepatopancreatic necrosis disease. Other bacteria including rickettsia, Wolbachia, Rickettsiella, Aquirickettsiella, Aerococcus viridans, and Spiroplasma spp. also cause disease. Finally, shell disease syndrome is a disease of many crustaceans where the integument is eroded by a community of bacteria arising from dysbiosis in the normal members of the integumentary microbiome. One form of the disease, epizootic shell disease, is an important disease of lobsters (Homarus americanus) in the USA. Treatment and control strategies for disease limitation are described.