Electricity and magnetism are interrelated and exist in a complementary fashion. Any conductor carrying electrical current has an associated magnetic field. A magnetic field can induce voltages or currents in a conductive medium exposed to the field. Altering one changes the other consistent with certain principles of electromagnetic dependency. Electrical circuits are carriers of electricity as well as propagators of magnetic fields. In many pieces of electrical apparatus, the relationship between electrical current and magnetic field is put to productive use. Some examples of utilizing the electromagnetic principle are generators, motors, transformers, induction heating furnaces, electromagnets, and relays, to mention just a few. Everyday lives depend heavily on electromagnetism. In the area of power quality, the useful properties of electromagnetism are not a concern; rather, the interest is in how electromagnetic phenomena affect electrical and electronic devices in an adverse manner. The effect of electromagnetism on sensitive devices is called electromagnetic interference (EMI) and is a rather complex subject. Many voluminous books are available on this subject, and each aspect of EMI is covered in depth in some of them. Here, some of the essential elements of EMI will be discussed in order to give the reader the basic understanding necessary to be able to identify problems relating to this phenomenon.