The article presents an information integration theory of consciousness by Giulio Tononi. The theory posits that consciousness arises from the capacity of a system to integrate information. This is supported by two key phenomenological properties of consciousness: differentiation, the availability of a large number of conscious experiences, and integration, the unity of each experience. The quantity of consciousness is measured by the Φ value of a complex, which represents the amount of causally effective information that can be integrated across the informational weakest link of a subset of elements. A complex is a subset of elements with Φ > 0 that is not part of a subset with higher Φ. The quality of consciousness is determined by the informational relationships among the elements of a complex, which are specified by the values of effective information among them. Each conscious experience is specified by the value of the variables mediating informational interactions among the elements of a complex at any given time. The theory accounts for several neurobiological observations concerning consciousness, including the association of consciousness with certain neural systems, the influence of unconscious processes on conscious ones, the reduction of consciousness during dreamless sleep and generalized seizures, and the time requirements on neural interactions that support consciousness. The theory also implies that consciousness is a fundamental quantity, graded, present in infants and animals, and that conscious artifacts can be built. The theory suggests that consciousness is related to the ability to integrate information across a characteristic spatio-temporal scale. The capacity to integrate information is measured by the Φ value of a complex, which is determined by the effective information between subsets of elements. The effective information matrix captures the informational relationships within a complex, defining the qualia space. The structure of this space reflects the informational relationships, and the quality of conscious experience is determined by the informational relationships within and between cortical areas. The theory also specifies that each conscious experience is determined by the activity state of the elements of a complex at a given time. The state diagram illustrates how different activity states correspond to different conscious experiences. The theory predicts that changes in the quality and repertoire of sensations due to perceptual learning correspond to a refinement of the informational relationships within and between appropriate cortical areas. The theory also suggests that informational relationships outside a complex do not contribute directly to the quality of conscious experience of that complex.The article presents an information integration theory of consciousness by Giulio Tononi. The theory posits that consciousness arises from the capacity of a system to integrate information. This is supported by two key phenomenological properties of consciousness: differentiation, the availability of a large number of conscious experiences, and integration, the unity of each experience. The quantity of consciousness is measured by the Φ value of a complex, which represents the amount of causally effective information that can be integrated across the informational weakest link of a subset of elements. A complex is a subset of elements with Φ > 0 that is not part of a subset with higher Φ. The quality of consciousness is determined by the informational relationships among the elements of a complex, which are specified by the values of effective information among them. Each conscious experience is specified by the value of the variables mediating informational interactions among the elements of a complex at any given time. The theory accounts for several neurobiological observations concerning consciousness, including the association of consciousness with certain neural systems, the influence of unconscious processes on conscious ones, the reduction of consciousness during dreamless sleep and generalized seizures, and the time requirements on neural interactions that support consciousness. The theory also implies that consciousness is a fundamental quantity, graded, present in infants and animals, and that conscious artifacts can be built. The theory suggests that consciousness is related to the ability to integrate information across a characteristic spatio-temporal scale. The capacity to integrate information is measured by the Φ value of a complex, which is determined by the effective information between subsets of elements. The effective information matrix captures the informational relationships within a complex, defining the qualia space. The structure of this space reflects the informational relationships, and the quality of conscious experience is determined by the informational relationships within and between cortical areas. The theory also specifies that each conscious experience is determined by the activity state of the elements of a complex at a given time. The state diagram illustrates how different activity states correspond to different conscious experiences. The theory predicts that changes in the quality and repertoire of sensations due to perceptual learning correspond to a refinement of the informational relationships within and between appropriate cortical areas. The theory also suggests that informational relationships outside a complex do not contribute directly to the quality of conscious experience of that complex.