Аннотация:The origin of ferroelectricity in smectic liquid crystals is attributed to the chirality of their molecules. The chirality reduces the space symmetry and leads to the helical (helicoidal) spatial distribution of molecular axes in ferroelectric and antiferroelectric liquid crystals (FLCs and AFLCs), called a helical structure, or helical nanostructure, if its period is much less than any wavelength of visible light. Deformations of FLCs and AFLCs helical structures under the applied electric field E lead to the emergence of a number of specific electro-optical effects. This review analyzes the main results of experimental and theoretical studies of various electro-optical manifestations of FLCs and AFLCs helical nanostructures deformations, which are already used to develop displays and photonic devices of a new generation.