Eriophyoid mites are a group of phytoparasites of high economic importance due to their ability to transmit phytopathogens and cause the development of various plant malformations including galls. Chemical compounds of mite saliva injected into plant cells and the reaction of the plant cell genome play the crucial role in the gall formation process. Various triggers specific to plant DNA (e.g. exogenous phytohormones) and pathogenic microbes may be the factors inducing the gallogenesis. The process of gall formation is a complex growth reaction induced in the epidermal cells. Mechanisms of the gallogenesis induced by eriophyoids are studied very insufficiently. The analysis of the available literary data shows that malformations caused by eriophyoids on plants significantly vary in shape, topography, and longevity and may have different etiologies. Differences in the shape of a gall depend, first of all, on the mite species; plants, however, demonstrate limited number of gall types. Clarified classification of galls induced by eriophyoid mites is proposed. A gradual program for future studies is represented.