Principles of cryogenic techniques and gas cooling. Isentropic and isenthalpic cooling. The properties of Helium isotopes. Heat exchangers, expansion engines, dilution refrigerators. Atomic and nuclear adiabatic demagnetization. Low temperature thermometry. Type I and type II superconductors. Magnetic properties of superconductors. London model and phenomenological Landau-Ginsburg equations. Weak superconductivity (Josephson effect and SQUIDs). Cuprates and other families of new superconductive materials. Low dimensionality superconductors.