From the Concrete to the Abstract. This concise presentation of theoretical physics has the advantage over multi-volume works that the deep connections between the various fields can be grasped more easily. The selection of topics highlights the many interrelations of both physical and mathematical nature. In addition to emphasizing overarching principles, the most important and profound results of recent theoretical physics are presented. This includes, in electrodynamics, wave solutions and radiation problems; in quantum theory, the separation of states and observables, spin and general two-state systems, coherence and decoherence, as well as entanglement and Bell's inequalities. The study of physics progresses from the concrete to the abstract. In this sense, this textbook builds on the modern foundational lectures in physics and the associated materials.