Modern Problems in Condensed Matter Sciences, Volume 14.2: Incommensurate Phases in Dielectrics, 2: Materials offers a physical picture of incommensurate insulators and gives readers an idea how experimental techniques can be used to study the dynamic and static properties of incommensurate systems on a microscopic level. The selection first offers information on the modulated phases in thiourea and incommensurate phase of quartz and barium sodium niobate (BSN). Discussions focus on the characteristics of the incommensurate phase in BSN, thermal hysteresis and relaxation effects, macroscopic symmetry breaking and related anomalies, properties of quartz and the discovery of the incommensurate phase, and dynamical properties. The text examines the incommensurate phases in an aromatic molecular crystal, including symmetry properties, molecular nature of the structural instability, satellite reflections, and excitations in incommensurate phases. The publication ponders on the incommensurate structures in liquid crystals, as well as liquid crystals and effects of incommensurability; incommensurate structures in cholesterol and sematic liquid crystals induced by external fields; incommensurate flex electric structure in hematic liquid crystals; and incommensurate sematic structures as polymorphous modifications. The selection is a vital reference for researchers interested in the incommensurate phases in dielectrics.