The auditory system of monkeys is composed of a complex network of interconnected subcortical nuclei and cortical areas. At the subcortical level, the structure resembles that of non-primate mammals, but the cortical organization is distinct. In monkeys, the ventral nucleus of the medial geniculate complex projects to a core of three primary-like auditory areas (AI, R, and RT), forming the first stage of cortical processing. These areas interconnect and project to adjacent regions in the opposite hemisphere and to a surrounding array of eight belt areas, which form the second stage. The belt areas then project to a lateral parabelt region, which constitutes the third stage of cortical processing. The parabelt region distributes information to adjoining auditory and multimodal regions of the temporal lobe and to four functionally distinct regions of the frontal lobe. Histochemically, chimpanzees and humans share an auditory core similar to that of monkeys. The auditory cortex of monkeys includes at least 20 interconnected areas or multimodal regions, with a hierarchical structure involving at least four distinct levels of processing. Information is distributed widely within levels, between areas of the same level in opposite hemispheres, and between levels. The existence of multiple areas at the primary level suggests overlapping functions, allowing the system to compensate for lesions that leave some areas intact. However, extensive damage to any level would be devastating due to the serial nature of processing.The auditory system of monkeys is composed of a complex network of interconnected subcortical nuclei and cortical areas. At the subcortical level, the structure resembles that of non-primate mammals, but the cortical organization is distinct. In monkeys, the ventral nucleus of the medial geniculate complex projects to a core of three primary-like auditory areas (AI, R, and RT), forming the first stage of cortical processing. These areas interconnect and project to adjacent regions in the opposite hemisphere and to a surrounding array of eight belt areas, which form the second stage. The belt areas then project to a lateral parabelt region, which constitutes the third stage of cortical processing. The parabelt region distributes information to adjoining auditory and multimodal regions of the temporal lobe and to four functionally distinct regions of the frontal lobe. Histochemically, chimpanzees and humans share an auditory core similar to that of monkeys. The auditory cortex of monkeys includes at least 20 interconnected areas or multimodal regions, with a hierarchical structure involving at least four distinct levels of processing. Information is distributed widely within levels, between areas of the same level in opposite hemispheres, and between levels. The existence of multiple areas at the primary level suggests overlapping functions, allowing the system to compensate for lesions that leave some areas intact. However, extensive damage to any level would be devastating due to the serial nature of processing.