"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 core of this proposal is to gain insight in the processes that are of major relevance for the solar dynamo by novel and improved methods of helioseismology. The analyses go 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 will fully exploit the unique properties of deeply penetrating seismic waves on the Sun. In this way unprecedented knowledge about the key processes involved in the deep seated origin of solar activity will be gained. By a paradigm change in global helioseismology, this includes for the first time full information on the structure of the meridional circulation and the magnetic field throughout the Sun. Moreover, three-dimensional views on the tachocline region in 200Mm depth and highly resolved seismic maps of the flow and sound speed variations in the sub-surface layers of the Sun present a highly innovative approach to understand the causes for solar activity on short time-scales. The results obtained will be 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."