Stirling engines are heat engines that, unlike Otto and diesel engines, are not limited to a specific fuel but convert externally supplied thermal energy from various sources into mechanical energy (and vice versa). Since heat from solar energy and even low-temperature waste heat can also be utilized and refined, this technically demanding engine has gained increasing attention in recent years. The author provides an overview of the fundamentals, technology, and designs of Stirling engines, which are predicted to have a bright future. He discusses the advantages and disadvantages of different engine concepts, highlights the development needs, and informs about the machines currently available. This serves as an introductory resource for engineers, students, and those with technical interests, complete with a detailed manufacturer and literature directory.