Lecture summary: The WTO Agreement on TBT (Technical Barriers to Trade) aims at taming NTBs (nontariff barriers), the main instrument segmenting markets nowadays. Some of the terms used in TBT to flesh out the commitments undertaken are borrowed from the GATT, and some originate in the modern regulatory reality as expressed through SDOs (standard-development organizations). The TBT does not share a copy-cat function with the GATT, though. Alas, the WTO Appellate Body, by understanding words as ‘invariances’, e.g., interpreting them out of context (without asking what is the purpose for the TBT?), has not only exported its GATT case law, but also misapplied it into the realm of TBT, and ended up with significant errors. In what follows, we explain why the current approach is erroneous, and advance an alternative understanding, which could help implement the TBT in a manner faithful to its negotiating intent, and objective function. Petros C. Mavroidis is Edwin Parker Professor of Law at CLS. Acted as chief reporter for the American Law Institute study on International Trade Law: the WTO. His latest major publication is The Regulation of International Trade, MIT Press, 2016.