The aim of this work is to estimate the relationship between tariff barriers and trade growth at the world level applying a long-term approach and comparing different trade regimes. At the same time it aims at giving useful insights to assess the effectiveness of the current multilateral trading system in fostering international trade. The distinctive feature of this study is the use of a long term data set concerning tariffs and trade of twenty-three countries (which account for over 60 per cent of world trade of the entire period) for the 1870-2000 time span. Using times series and panel data analyses the author shows as the existence of a long run relationship between tariffs reduction and trade growth at the world level is quantitatively noteworthy exclusively in the period before the Second World War while it weakens starting from 1950. The empirical results do not controvert the role that the GATT/WTO system has played in the tariff reduction process but underline as its main effect has been linked to the creation of a rule-based environment governing global trade relations, through which uncertainty was reduced and the spread of best practices promoted.