This lecture introduces dielectric materials as a special class of insulators that can be polarized by an applied electric field. It covers the definition of dielectric, temperature dependence, and examples of materials with permanent electric dipole moments. The potential function of an electric dipole moment and the alignment of a dipole in an electric field are also discussed, along with the concept of multiple expansions to calculate electric fields. The lecture concludes with the calculation of electrostatic potential energy for a dipole in an electric field.