AbstractThe United Nations with its Food Systems Summit 2021 and member countries seek to alter food systems to be healthier, safer, more sustainable, efficient and equitable. This chapter informs about concepts and definitions of food systems and the determinants of their change. To foster a clear understanding of food systems, especially regarding the UN Food Systems Summit and potential follow up to it, we first present a general food systems concept. We then introduce a concept based on science that provides a definition that the UN Food Systems Summit could use with the five goal-oriented Action Tracks (serving SDG2) and their interlinkages. We suggest a food system definition that encompasses food systems thinking and the broad set of actors and drivers, embedding the concept of sustainability within it.