This study investigates the unique features of adult human astrocytes compared to those of rodents, focusing on their microanatomic differences. Human protoplasmic astrocytes are 2.6 times larger in diameter and extend 10 times more GFAP-positive primary processes than their rodent counterparts. In cortical slices, human astrocytes propagate Ca2+ waves at a speed of 36 μm/s, approximately four times faster than in rodents. Human astrocytes also transiently increase cystosolic Ca2+ in response to glutamatergic and purinergic receptor agonists. The human neocortex contains several anatomically defined subclasses of astrocytes not found in rodents, including varicose projection astrocytes and interlaminar astrocytes. Varicose projection astrocytes, found only in higher-order primates, have long fibers with regularly spaced varicosities. Interlaminar astrocytes, abundant in the superficial cortical layers, extend long processes without varicosities to cortical layers 3 and 4. Human fibrous astrocytes are larger than rodent counterparts but are structurally similar. These findings suggest that the increased complexity and diversity of human astrocytes contribute to the enhanced functional competence of the adult human brain.This study investigates the unique features of adult human astrocytes compared to those of rodents, focusing on their microanatomic differences. Human protoplasmic astrocytes are 2.6 times larger in diameter and extend 10 times more GFAP-positive primary processes than their rodent counterparts. In cortical slices, human astrocytes propagate Ca2+ waves at a speed of 36 μm/s, approximately four times faster than in rodents. Human astrocytes also transiently increase cystosolic Ca2+ in response to glutamatergic and purinergic receptor agonists. The human neocortex contains several anatomically defined subclasses of astrocytes not found in rodents, including varicose projection astrocytes and interlaminar astrocytes. Varicose projection astrocytes, found only in higher-order primates, have long fibers with regularly spaced varicosities. Interlaminar astrocytes, abundant in the superficial cortical layers, extend long processes without varicosities to cortical layers 3 and 4. Human fibrous astrocytes are larger than rodent counterparts but are structurally similar. These findings suggest that the increased complexity and diversity of human astrocytes contribute to the enhanced functional competence of the adult human brain.