This chapter introduces the fundamental concepts of superconductivity. It begins with the conditions for superconductivity, including persistent currents and critical fields and currents. The chapter then discusses the difference between a perfect conductor and a superconductor, focusing on the Meissner effect, which excludes magnetic fields from the superconducting material. The Meissner effect is explained through the interaction of magnetic fields with perfect conductors and the mathematical description provided by the London equations and penetration depth. The chapter also delves into macroscopic quantum effects, such as the macroscopic wave function and current, the quantization of magnetic flux, and the measurement of the flux quantum. It covers the Josephson effect and the SQUID (Superconducting Quantum Interference Device), which are key tools for studying superconductivity. Finally, the chapter includes a summary and answers to questions, highlighting the levitation effect and the potential applications and mechanisms governing the behavior of electrons in superconducting materials.This chapter introduces the fundamental concepts of superconductivity. It begins with the conditions for superconductivity, including persistent currents and critical fields and currents. The chapter then discusses the difference between a perfect conductor and a superconductor, focusing on the Meissner effect, which excludes magnetic fields from the superconducting material. The Meissner effect is explained through the interaction of magnetic fields with perfect conductors and the mathematical description provided by the London equations and penetration depth. The chapter also delves into macroscopic quantum effects, such as the macroscopic wave function and current, the quantization of magnetic flux, and the measurement of the flux quantum. It covers the Josephson effect and the SQUID (Superconducting Quantum Interference Device), which are key tools for studying superconductivity. Finally, the chapter includes a summary and answers to questions, highlighting the levitation effect and the potential applications and mechanisms governing the behavior of electrons in superconducting materials.