With the reduction in tariff barriers, Non-tariff and behind-the-border measures (NTM and BTB) have increased in importance. This paper surveys the state of knowledge with the view to drawing implications for policy suggestions to reduce those NTM barriers that are welfare reducing. Following a description of data bases and their shortcomings, the paper reviews the state of understanding on the effects of NTMs on trade flows. The more difficult issue of translating these effects into welfare implications are covered next. The paper concludes with different approaches at reducing NTMs.