This study investigates the effects of selected sanitary and phytosanitary measures (SPS) and technical barriers to trade (TBT) on agricultural trade between the United States and the European Union (EU). It identifies data, methodological, and conceptual challenges to quantify such non-tariff measures (NTM) in the context of free-trade agreements. An empirical strategy combining market analysis with gravity model econometric methods is used to quantify the extent of protection afforded by major NTMs in U.S.-EU agricultural trade. In most of the commodities investigated with specific SPS/TBT concerns, estimated ad valorem tariff equivalents (AVE) of NTMs were found to be considerably higher than existing tariffs. EU NTMs on U.S. poultry, pork, and corn were found to have the most trade-impeding effects, with estimated AVE effects of 102, 81, and 79 percent, respectively; EU NTMs on U.S. beef, vegetables, and fruits were also found to be significant. The AVE effect of U.S. NTMs on EU exports ranges from 37 percent for vegetables to 45 percent for fruits.