As explained in Fig. 1.2 , the ultimate goal of this book is to explain the origin of the ‘coupling between spin and magnetic fields’. This derivation will be discussed in Chap. 7 through relativistic quantum mechanics. In this theory, the electromagnetic field appears naturally. However, without describing the ‘basic mathematical framework of electromagnetism, the explanation in Chap. 7 will seem abrupt. With the foundational knowledge from Chap. 2 , the concepts required to understand this are almost within reach. This chapter serves to provide the necessary fundamentals of electromagnetism for the logical developments in subsequent chapters. First, as an application of the field analysis introduced in the latter part of the previous chapter, we will formulate several concepts. We will then cover the differential laws for electrostatic fields and magnetostatic fields. Next, we will discuss electromagnetic induction and explore how the differential laws for electrostatic and magnetostatic fields are modified when dynamics are considered.