Maximilian Scheurer presents a method for modeling excited states in atomistic, heterogeneous environments. The method utilizes the polarizable embedding (PE) model to mimic electrostatic and polarization interactions of a molecule with its environment. For high-level modeling of the molecule's excited states, the algebraic-diagrammatic construction scheme for the polarization propagator (ADC) is employed. The presented work outlines the theoretical foundations of PE and ADC and the combination of both methods, termed PE-ADC. The accuracy of PE-ADC is tested, and the charge-transfer (CT) excitation in the dodecin protein is studied. This book presents a comprehensive elaboration on the new PE-ADC method and a state-of-the-art application of PE-ADC to a photo-biochemical process.