This book, together with the three other volumes, offers a clear and comprehensive approach to theoretical physics for the entire Bachelor's program. Highlights: Theoretical derivations are linked with characteristic examples, their solutions, typical applications, and clearly illustrated in diagrams. The required mathematics is derived in a physical context and explained transparently. Contents: Principles of Classical Physics – Limits of Classical Physics – Beginnings of Quantum Theory: Matter Waves – Quantum Theory of a Particle – Operators and Expectation Values – Measurements and Probabilities – Particles under the Influence of External Forces – Fundamentals of Scattering Theory – The Hilbert Space – Operators in Hilbert Space – The Time Evolution Operator – Particle Number Representation for Fermions – Particle Number Representation for Bosons – Quantization of the Radiation Field: Photons – Formal Scattering Theory – The Hartree-Fock Approximation – Superconductivity in the BCS Model Target Audience: This book is especially suitable for Bachelor's students in their second or third year. Prerequisites: Mathematical prerequisites include knowledge of analysis, linear algebra, and complex function theory. The Author: Wolfgang Cassing is a retired Professor of Theoretical Physics at the Justus-Liebig-University Gießen. His expertise lies in phase space dynamics of classical and quantum many-body systems, which also features in his scholarly book "Transport Theories for Strongly-Interacting Systems". This textbook series Theoretical Physics Compact also includes Classical Mechanics, Electrodynamics, and Quantum Statistics and Thermodynamics.