Superconductivity has been found in a wide range of materials, including pure metals, alloys, compounds, oxides, and organic materials. Providing information on the basic principles, this Article discusses the theoretical background, types of superconductors, and critical parameters of superconductivity. It discusses the magnetic properties of selected superconductors and types of stabilization, including cryogenic stability, adiabatic stability, and dynamic stability. The Article also focuses on alternating current losses in superconductors, including hysteresis loss, penetration loss, eddy current loss, and radio frequency loss. Furthermore, the Article describes the flux pinning phenomenon and Josephson effects.