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Publisher Summary This chapter reviews that structural plasticity of astrocytes in the normally functioning brain is widespread. Two of the best-studied regions where structural plasticity occurs are the supraoptic nucleus (SON) and posterior pituitary. It discusses the recent developments in understanding of how this structural remodelling, including new finding that show microglia also participate in structural plasticity of the SON. The chapter also introduces other brain areas, where structural plasticity of astrocytes has been demonstrated. Structural plasticity of glia, predominantly that of astrocytes, occurs throughout the nervous system. Sites, where structural plasticity of astrocytes has been documented in normal brains include the hippocampus with long term potentiation induction in the suprachiasmatic nucleus across the diurnal cycle, in the cerebellar cortex with motor learning in the arcuate nucleus of the rat and monkey, across changing estrogen levels, and extensively, in the hypothalamo-neurohypophyseal system (HNS) in response to diverse conditions leading to the synthesis and release of the peptides oxytocin (OX) and vasopressin (VP). The chapter concludes that the factors that are investigated in the SON of the hypothalamus include reorientation of astrocytes, reentry of glial cells into the cell cycle, downregulation of morphoregulatory molecules, dissolution of the basal lamina, changes in the GFAP, concomitant changes in expression of GFAP message, and changes in the population of resident microglia.