The development of modern technologies also increases the need for more and more sensitive measurement methods. In the field of magnetic field measurement, the use of physical effects, such as the anisotropic or "giant" magnetoresistance effect (AMR or GMR) or the Josephson effect, has proven to be very promising. SQUIDs (“Superconducting Quantum Interference Device”) are the most sensitive magnetic field sensors available today. They achieve a resolution of the order of a few femtoteslas. The functioning of a SQUID is based on two effects that only occur with superconductivity: flux quantization and the Josephson effect. This practical experiment is intended to give a theoretical and practical introduction to the basics of handling SQUID.