Book excerpt: Here, leading scientists present an overview of the most modern experimental and theoretical methods for studying electronic correlations on surfaces, in thin films and in nanostructures. In particular, they describe in detail coincidence techniques for studying many-particle correlations while critically examining the informational content of such processes from a theoretical point viewpoint. Furthermore, the book considers the current state of incorporating many-body effects into theoretical approaches. Covered topics: -Auger-electron photoelectron coincidence experiments and theories -Correlated electron emission from atoms, fullerens, clusters, metals and wide-band gap materials -Ion coincidence spectroscopies and ion scattering theories from surfaces -GW and dynamical mean-field approaches -Many-body effects in electronic and optical response