Maxwell's Equations, Photons and the Density of States -- Interaction of Light with Matter -- Ensemble of Uncoupled Oscillators -- The Concept of Polaritons -- Kramers-Kronig Relations -- Crystals, Lattices, Lattice Vibrations and Phonons -- Electrons in a Periodic Crystal -- Excitons, Biexcitons and Trions -- Plasmons, Magnons and some Further Elementary Excitations -- Optical Properties of Ph…