Starting from a brief introduction to the Meissner effect and other defining properties of superconductivity, Chapter 1 recapitulates the phenomenological theories, including the two-fluid model and the Ginzburg-Landau theory, and the groundbreaking microscopic theory of Bardeen-Cooper-Schrieffer for describing this macroscopic quantum phenomenon. The Cooper pairing and other basic concepts of superconductivity, such as the gap function, off-diagonal long-range order, quasiparticle excitations, coherence length, penetration depth, type-I and type-II superconductors, and phase fluctuations are also introduced, followed by a summary on the classification and experimental identification for the pairing symmetry of high-Tc superconductors.