The technical requirements of mobile location-based games have been met sufficiently well to make location-based mobile games an everyday object. Games like Ingress or Pokémon GO have experienced a huge popularity. Hence, the question arises how the obvious attraction of these games can be used to achieve goals other than entertainment, such as learning. This article describes the basic scientific background of a workshop of the ICEC-JCSG 2019 for the development of design principles for serious mobile location-based games. First the game types involved are defined, then relevant design principles are identified and presented providing a basis to substantiate design guidelines in the workshop and contribute to the purposeful design of mobile location-based games.