In 1834, Michael Faraday introduced the concept of dielectric materials and their polarization for the first time. The chapter outlines the evolution of theories related to depolarization fields, macroscopic and local electric fields, and atomic polarizability. Clausius and Mossotti’s relation connecting dielectric constant and polarizability is discussed, along with the Lorentz-Lorenz relation. Theories of different polarizability types, the Kramers–Kronig relations, and Lyddane-Sachs-Teller relation are presented. Optical theories by Drude and Lorentz, and empirical relations like the Hagen-Rubens formula for reflectivity, are also included. The chapter discusses the discovery of pyroelectric and piezoelectric materials and focuses in detail on ferroelectric materials—their history, theories (dipolar, molecular, lattice dynamical), and phase transitions. It concludes with the description of soft phonon modes and electric domains observed experimentally in ferroelectric materials.