H-alpha spectroheliograms revealed already in the early twentieth century the beauty and the huge variety of magnetic structures in the chromosphere. However, a comprehensive description of this important layer, coupling the photosphere to the corona, is still missing. The key for a deeper understanding of the chromosphere lies in the reliable determination of the vector magnetic field. The low magnetic field strengths combined with the complexity of non-LTE line formation require a close interplay between advanced atomic physics involving modeling and sophisticated observational techniques and instrumentation. This proposal addresses the problem of measuring the magnetic field topology in the chromosphere. The applicant's knowledge on the theory of the scattering polarization and its modification due to the Hanle effect will be combined with observational data, analysis methods and powerful inversion codes available at the MPS. Therefore, the applicant and host organization will form a symbiotic partnership. The equipment of the host to achieve the goals of the project is excellent: MPS has access to powerful workstation clusters. As a partner institute of the German solar telescopes on Tenerife, MPS has guaranteed observing time. Knowledge on data analysis and inversion techniques is excellent. Including the applicant's experience in Hanle diagnostics will result in a fruitful and productive cooperation and open excellent career opportunities to the applicant.