Aphid-induced galls provide the gall-inducing organisms with shelter from climatic adversities, safe places from predators, and access to the elaborated sap that circulates through the phloem. These galls are formed by tissue hyperplasia and cell hypertrophy, especially in the vascular bundles. They are induced by a single wingless individual, which initiates a sequence of parthenogenetic generations and can be categorized into three morphofunctional patterns: closed galls, open galls, and pseudogalls. In the open galls, a hole known as the closure zone is usually covered by trichomes that seal the gall entrance, from which winged individuals will emerge by the end of the maturation phase. Besides an outer epidermis, aphid gall walls are composed of an outer storage parenchyma, with altered cell shapes, functions, and sizes, when compared to the host organ. In some galls, there is a single row of vascular bundles, in others, two rows of specular vascular bundles with the xylem or the phloem cells facing the chamber, depending on the induction surface. The inner epidermis, lining the gall lumen or gall chamber, is often multiseriated, without holes or with dimples related to the reabsorption of honeydew in closed galls, preventing drowning of galling aphids. From a physiological point of view, aphid-induced galls seem to be active sinks, accumuluating metabolites, which can be related to the survivorship of the gall inducers. Aphid-galls are comprehensive study models, revealing insights into plant development modulation and phylogenetic relationships, with potential applications in assessing protective features and understanding the comparative effects of insect stimuli on host plant organ physiology.