In this introductory chapter we explain why the classical picture of physics turned out to be untenable and should be replaced by a new paradigm, namely Quantum Physics. To provide a broader perspective, we tell a fictional history of how the transition from the classical to the quantum description of reality could have occurred more naturally in the form of deformation quantization. Then we present the ideal experiments which motivate the most fundamental principle of Quantum Physics, the superposition principle, and then present the mathematical formulation of the principle which identifies quantum states with rays in a complex vector space, and yield the first consequences of this principle. We end the chapter with a discussion of the open quantum systems and the qualifications that the superposition principle requires in this more general context.