An insulator, also called a dielectric, is a material that resists the flow of electric current. An insulating material has atoms with tightly bonded valence electrons. These materials are used in parts of electrical equipment, also called insulators or insulation, intended to support or separate electrical conductors without passing current through themselves. Some materials such as glass, paper or Teflon are very good electrical insulators. This book presents topical research data in the study of insulators, including design and development of a new type of ferromagnetic insulator; insulator inspection technologies; high-k dielectric insulators used in low-voltage organic field-effect transistors; the electrodynamics of Mott insulators and insulator-to-metal transitions; and the leakage current on high voltage contaminated insulators.