Owing to economic considerations, there has been renewed interest in the use of coal as a shipboard fuel. To utilize coal aboard ship again required only the application of technology developed and proven ashore over the past 30 years since coal was last used extensively at sea. The development of a modern coal-fired marine boiler was thus possible in a relatively short time. The paper discusses the state of the art of marine coal-fired boilers, including economics, alternative firing systems, boiler performance, design philosophy, and system design.