Dual eye-tracking (DUET) is at the confluents of cognitive (and social) psychology and computer science. DUET is a novel methodology to explore the socio-cognitive processes underlying collaboration. The basic aims of DUET are to better understand, through gaze indicators, a socially distributed cognitive system and to support collaboration by real time gaze display of collaborators. We are interested in finding whether and how patterns of eye-movements can reflect the cognition underlying collaboration. This paper concentrates on the major motivations, methodological challenges and the future aspects of DUET.