 For 1989–90 he was a scholar-in-residence of Pre-Columbian Studies at Dumbarton Oaks Research Library and Collection, with a research project entitled "Warfare and the Mesoamerican Past".In 1997–98 Hassig spent a year as Resident Scholar under the Weatherhead Fellowship program at the School of American Research in Santa Fe, New Mexico, with a primary focus on researching the Aztec calendar.In the 1999 United Kingdom academic year, Hassig was awarded one of the two residential Visiting Fellowships offered annually by the Sainsbury Research Unit at the Sainsbury Centre for Visual Arts, University of East Anglia, Norwich, towards the study of 'Aztec thought and culture'.