Gall induction involves the reprogramming of plant meristematic cells, changing the rates and patterns of division, expansion, and differentiation, culminating in gall morphogenesis. As apical and axillary meristems determine plant organogenesis, gall morphogenesis also requires the involvement of meristems through their overactivation or impairment at the induction site. Galls induced on stem buds involve changes in existing apical or axillary meristems, whereas those induced on other plant parts usually trigger parenchymatic cell responses. In such cases, parenchyma cells may redifferentiate into ectopic meristems during gall development, whose cell divisions involve the galling organisms, presenting sites with different cell division axes. The varying expansion rates lead to either tissue invagination or the thickening of plant petioles, midribs, and stems, ultimately resulting in the various gall morphotypes found in nature. By the time of gall maturation, some morphotypes may maintain their meristems active, or the parenchyma cells may redifferentiate into cambium-like cells, adding new cell layers to the outer parenchyma or to the nutritive tissues. The involvement of the vascular cambium in galls enhances the differentiation of secondary xylem and phloem cells, improving the flux of water and photoassimilates crucial for gall development, sometimes in distinct proportions, indicating peculiar metabolic demands. The renewal of gall cells supports the longevity of the gall cycle, and procambium neoformation guarantees the connection of galls and host organ vascularization, which is responsible for the trafficking of molecules from the original and ectopic meristems to gall tissues.