An introduction to the physics of electrical insulation, this book presents the physical foundations of this discipline and the resulting applications. It is structured in two parts. The first part presents a mathematical and intuitive approach to dielectrics; various concepts, including polarization, induction, forces and losses are discussed. The second part provides readers with the keys to understanding the physics of solid, liquid and gas insulation. It comprises a phenomenological description of discharges in gas and its resulting applications. Finally, the main electrical properties of liquids and solids are presented, in order to explain the phenomena of electrical degradation, dissipation and breakdown. Contents 1. Mathematical Examination of Dielectrics 2. Physical Examination of Dielectrics Appendix 1. List of Figures Appendix 2. List of Symbols Appendix 3. List of Useful Values Appendix 4. Reminder about Dielectric Spectroscopy Appendix 5. Reminder about Transitory Currents