Walter Hellerstein is Distinguished Research Professor and Shackelford Professor of Taxation Emeritus at the University of Georgia Law School, Athens, Georgia, USA. He is co-author of State Taxation, vols. I & II (3rd ed. (updated tri-annually); State and Local Taxation (10th ed. 2014); and Taxing Global Digital Commerce (2013), and has authored more than 100 journal articles. He serves as an academic advisor to the OECD’s Working Party No. 9 on Consumption Taxes and is a member of the Working Party’s Technical Advisory Group on the VAT/GST Guidelines.