In this chapter, we present the main ideas behind the FEM based on a general three-dimensional acoustic problem. Section 5.2 describes the various steps of the FEM. Section 5.3 discusses convergence considerations. Section 5.4 presents several examples to illustrate the concepts discussed in Section 5.2. Finally, Section 5.5 formulates the acoustic and vibratory indicators commonly used in the field of vibroacoustics. The reader may refer to several references (Batoz and Dhatt 1990; Petyt 1990; Imbert 1991; Bathe 1996; Craveur 1997; Géradin and Rixen 1997; Hughes 2000; Zienkiewicz and Taylor 2005) for more details about the FEM in general.