Explore the intricate relationship between Eisenstein series and the cohomology of congruence groups in this 55-minute lecture by Joachim Schwermer from the University of Vienna and Max Planck Institute for Mathematics. Delve into advanced mathematical concepts as part of the "Theta Series: Representation Theory, Geometry, and Arithmetic" program held at the Fields Institute. Gain insights into the intersection of representation theory, geometry, and arithmetic through this in-depth presentation, which contributes to the broader understanding of theta series and their applications in various mathematical domains.