Piezoelectricity is a form of electricity that occurs when materials with piezoelectric properties are subjected to external mechanical stress. A key parameter associated with piezoelectricity is the electric field. This chapter describes the basic physical properties of the electric field both in vacuum and in the dielectric. The electric field equations necessary for further considerations are derived and summarised step by step. In particular, the difference between macroscopic (mean) and microscopic (local) field quantities is explained. For this purpose, the basic experimental results are used at the beginning, which lead to the formulation of the corresponding general equations. The chapter concludes with the formulation of the energy density of the electrostatic field on the basis of macroscopic field quantities in isotropic and anisotropic dielectrics, including the lead zirconate-lead titanate system PZT.