Recall that the maximal planar graphs are a class of planar graphs with the maximum number of edges, which have been studied extensively since the late 19th century due to the fact that the Four-Color Conjecture can be studied sufficiently for maximal planar graphs. In the subsequent chapters, we will present a series of results related to maximal planar graphs. This chapter mainly discusses the structures of maximal planar graphs by using the proof technique–discharging.