Gall development is characterized by changes in the three plant tissue systems. In the vascular system, a new xylem cellular pattern is influenced by plant hormones that induce alterations in diameter, frequency, arrangement of vessel elements, and the proportion of vascular fibers, axial and radial parenchyma. These changes are observed in galls induced in all plant organs and by different gall-inducing taxa. In addition to hormonal influence, the position of the gall in their host plant organ has been associated with changes in the vascular system, significantly impacting water conductivity in the regions adjacent to the galls. Consequently, compensatory mechanisms are triggered to ensure water supply. Among these mechanisms, the distinct pathways of vascular differentiation (procambium, vascular cambium, or parenchyma) and translocation via the symplast or apoplast in the parenchyma cells can ensure the supply of water and mineral salts to the gall developmental site. In this chapter, our objective was to revisit the changes observed in xylem cells in galls induced by different galling taxa, aiming to contribute to understanding the action of gall inducers on complex tissues. Furthermore, we highlight gaps in knowledge that can guide new questions and approaches to the xylem in galls.