Solar flares are sudden, explosive releases of the magnetic energy stored in the Sun. They often affect a wide range of solar regions: the corona, the chromosphere, and the photosphere, influencing their temperatures, densities, and magnetic fields. Space weather and thus its influence on the Earth is largely driven by flares, but their prediction and detailed mechanisms throughout the solar atmosphere are still unclear. The overall goal of this project is to understand the connections and interplay of different solar layers during flares. I propose to investigate the flare mechanisms with state-of-the-art methods by combining data from RHESSI, IBIS, Hinode, IRIS, and SDO. The combination of these data allows us to study the three-dimensional structure of the solar magnetic field and the free energy stored in the corona to estimate the potential for flares. This has rarely been attempted in the past because these different telescopes and spacecraft, observing methods, and analysis techniques require the combined expertise of different fields of heliophysics. With the applicant's strong background in polarimetry and the host institute's fundamental expertise with high-energy observations, I expect to derive a three-dimensional picture of flares, which will significantly improve our capabilities for space weather forecasting.