We start with a brief overview of ferroelectrics for the reader who is not veryfamiliar with ferroelectricity and piezoelectricity. You can refresh your currentfundamental knowledge through this section.Applications of “ferroelectrics” can be found in various devices such as high-permittivity dielectric capacitors, ferroelectric memories, pyroelectric sensors, piezo-electric devices, electro-optic devices, and PTCR (positive temperature coefficient ofresistivity) components. However, historically, with the existence of competitive ma-terials, ferroelectric devices often failed to be commercialized. In photo-sensors, forexample, semiconductive materials are superior to ferroelectrics in terms of responsespeed and sensitivity. Magnetic devices and flash memories are much more popularin the memory field, and liquid crystals (LCD) and light-emitting diodes (LED) aretypically used for optical displays. The commercialization failure was related to alack of systematic and comprehensive accumulation of knowledge on ferroelectricity,though we can recognize recent success in specific areas such as pyroelectric camerasand ferroelectric memories.This section covers the theoretical background of ferroelectric devices, beforefocusing on practical materials and typical applications, including (1) crystal struc-tures and ferroelectricity, (2) the origin of spontaneous polarization, (3) the originof field-induced strain, (4) piezoelectric constitutive equations, (5) ferroelectric ma-terials, and (6) applications of ferroelectrics. This section is based on my textbook,Ferroelectric Devices 2nd Edition.