M. marinum naturally infects fish and amphibians and causes diseases in these animals with pathological features similar to the human disease caused by M. tuberculosis. At the genetic and biochemical levels, M. marinum is closely related to M. tuberculosis. Because of these and other properties of M. marinum (such as its fast growth rate and convenient laboratory handing on the benchtop), M. marinum has been increasingly used as a model for studying M. tuberculosis pathogenesis. The protocols in this unit describe the methods for laboratory culturing (in liquid and solid media) and maintenance (subculturing, short- and long-term storage) of M. marinum and the methods for processing M. marinum for infection assays. Important parameters for culturing and maintaining M. marinum and its processing for infection assays are discussed in detail.