The big regional trade agreements such as the Transatlantic Trade and Investment Partnership, TTIP, could significantly affect the world trading system. How and to what extent will these agreements generate gains from trade and reduce transatlantic trade costs? And what will they mean for third parties? This policy brief reviews some of the recent analyses and discusses how the TTIP could usefully draw on the experience in the World Trade Organization, WTO, to enhance transparency, and the scope for third parties to raise issues related to regulatory barriers to trade.