Significant progress has been made in quantifying the effects of non-tariff measures since OECD commissioned its last major review of this topic in 1997. This paper reviews the literature of NTMs and assesses the different methods available. Additionally, the paper develops a series of questions to help determine which method of analysis is best given the interests of the researchers or policy makers. Of the possible avenues of future research, the trade costs approach is offered. This approach has the potential of shedding new light on the interactions among various policies and practices by assessing which areas offer the greatest potential for gains, and improving the precision of available estimates.