Mycobacterium marinum is being used increasingly as a model for understanding pathogenic mycobacteria. However, recently discovered differences between M. marinum and M. tuberculosis suggest that adaptation to specialized niches is reflected in unique strategies of pathogenesis. This review emphasizes the areas in which studying M. marinum has made contributions to the understanding of tuberculosis, as well as the potential for using characteristics unique to M. marinum for understanding general issues of host-pathogen interactions.