Humans interact with other people throughout their lives. This project aims to demonstrate that the complex social shaping of the human brain can be adequately tackled only by taking a leap from the conven-tional single-person neuroscience to two-person neuroscience. We will (1) develop a conceptual framework and experimental setups for two-person neuroscience, (2) apply time-sensitive methods for studies of two interacting persons, monitoring both brain and autonomic nervous activity to also cover the brain body connection, (3) use gaze as an index of subject s attention to simplify signal analysis in natural environments, and (4) apply insights from two-person neuroscience into disorders of social interaction. Brain activity will be recorded with millisecond-accurate whole-scalp (306-channel) magnetoencepha-lography (MEG), associated with EEG, and with the millimeter-accurate 3-tesla functional magnetic reso-nance imaging (fMRI). Heart rate, respiration, galvanic skin response, and pupil diameter inform about body function. A new psychophysiological interaction setting will be built, comprising a two-person eye-tracking system. Novel analysis methods will be developed to follow the interaction and possible synchronization of the two persons signals. This uncoventional approach crosses borders of neuroscience, social psychology, psychophysiology, psychiatry, medical imaging, and signal analysis, with intriguing connections to old philosophical questions, such as intersubjectivity and emphatic attunement. The results could open an unprecedented window into human human, instead of just brain brain, interactions, helping to understand also social disorders, such as autism and schizophrenia. Further applications include master apprentice and patient therapist relationships. Advancing from studies of single persons towards two-person neuroscience shows promise of a break-through in understanding the dynamic social shaping of human brain and mind.