Final Report Summary - ORIGIN (The Origin of Solar Activity) Solar activity impacts the near-Earth space environment and the Earth’s climate. It is caused by a magnetic field which varies over an 11-year cycle, the origin of which remained so far an unsolved puzzle for astrophysics. It is assumed that self-excited dynamos generate a complex, large-scale magnetic field in shear zones in the solar interior. Observational evidence for the physical conditions in these regions as well as for the large-scale flow components in the solar convection zone is marginal at best, but is urgently needed to explain the structure and evolution of the magnetic field.The major results of this project are the gain of insight on the processes that are of major relevance for the solar dynamo by novel and improved methods of helioseismology. The analyses went far beyond the state-of-the-art and are based on highly resolved velocity measurements on the Sun from NASA’s milestone missions SOHO and SDO as well as the instruments of the GONG network. Combining the advantages of innovative local helioseismology methods with an unconventional approach of global helioseismology the unique properties of deeply penetrating seismic waves on the Sun were exploited. In this way unprecedented knowledge about the key processes involved in the deep seated origin of solar activity were gained. By a paradigm change in global helioseismology, this included for the first time full information on the structure of the Sun’s meridional circulation, first estimates on the magnetic field configuration inside the Sun, and possibilities to probe the subsurface structure of active regions like sunspots.The results obtained are important for other disciplines, e.g. space weather applications to protect technological systems in space and on Earth, as well as predicting the influence of the Sun on Earth’s climate. Furthermore, stellar physics will strongly profit from the possibilities of estimating the interior stellar magnetic field from the stellar eigenoscillations.