Interoception refers to the ability to perceive, process, and interpret signals originating from within the body, such as heart rate, breathing, or temperature. It encompasses both unconscious processes that maintain homeostasis and the conscious perception of bodily states, which form the basis of emotions, self-regulation, and bodily self-awareness. Interoception enables the organism to respond adequately to changes in internal and external conditions, supporting emotional regulation and adaptive behavior. The key brain structure involved in interoceptive processing is the insular cortex, whose heterogeneous cytoarchitecture and extensive connections allow the integration of somatic signals with emotional, perceptual, and cognitive processes. Together with the anterior cingulate cortex, it forms the salience network, which monitors the relevance of stimuli and coordinates the activity of other large-scale brain networks. The article discusses current neurobiological findings on the functional organization of the insular cortex and its role in mental disorders characterized by disrupted interoceptive processing. Alterations in insular activity and functional connectivity have a transdiagnostic nature and may constitute a shared mechanism underlying dysfunctions observed in depression, anxiety disorders, schizophrenia, and eating disorders. In depression, insular activity tends to be decreased; in anxiety disorders, increased; in schizophrenia, connectivity between the salience network and other networks is impaired; and in eating disorders, activation patterns vary depending on the subtype. Interoception thus emerges as a process of fundamental importance for maintaining both physical and psychological balance.