This book provides a fundamental physical picture of various phenomena occurring in organic monolayers, dealing with dielectric, elastic, and electronic properties. The dielectric properties are discussed in terms of orientational order parameters, which are used to interpret the dielectric spectrum observed through Maxwell displacement current measurement and optical second harmonic generation measurement. The elastic theory of organic monolayers is based on that of liquid crystals and emphasis is placed on the interfacial effect when discussing the electronic properties of organic monolayers. The discussion in the book mainly concerns the structure dependence (dipole moment) and thickness dependence (interfacial effect) for various phenomena occurring in organic monolayers.