This chapter presents the Stern–Gerlach experiment as a concrete illustration of measurement, state collapse, and spin quantization. The chapter illustrates how discrete measurement outcomes emerge in quantum systems and how they are related to the mathematical structure of quantum states. The Stern–Gerlach experiments are approached with a classical mechanics perspective; observational results are presented to test hypotheses, and the falsification of classical hypotheses is used to motivate the need for quantum mechanics. All the experiments are then modeled using quantum mechanics to demonstrate agreement.