Classical electromagnetism is a well-established discipline. However, there remains some confusions andmisunderstandings with respect to its basic structures and interpretations. For example, there is a long-lasting controversy on the choice of unit systems. There are also the intricate disputes over the so-called EH or EB formulations. In some textbooks, the authors respect the fields E and B as fundamental quantities and understate D and H as auxiliary quantities. Sometimes the roles of D and H in a vacuum are totally neglected.