American and European lobsters are both high profile and high value animal species that provide significant economic value in the areas where they are landed. As such, it is important to understand the factors that contribute to the health of the animals and their populations, and how these animals can defend against pathogen impacts, especially the components of their immune systems. It is somewhat surprising to see that there is a considerable amount of published information on the immune systems other commercially important crustacean species such as warm-water marine and freshwater shrimp and crayfish, yet the is relatively little published material on the American and European lobsters. This review highlights the key areas of crustacean immune function and the published evidence as it relates to these important species. This includes; pattern recognition receptors, variable immune molecules, clotting factors, prophenoloxidase, hemocytes and antibacterial/anti-micorbial components.