Regulations flourish in modern economies, as requirements become more stringent in diverse and fundamental areas such as health, environment, safety, or financial security. Increasingly, these issues are taking centre stage in trade negotiations, since differences and inconsistencies may significantly hamper trade flows. While recent agreements have covered new grounds in this respect, on-going negotiations also show how difficult moving toward regulatory convergence is in practice. The Transatlantic negotiation is an obvious case in point. In addition to technical concerns, these difficulties have to do with the legitimacy of trade negotiations when it comes to influencing regulatory practices. Culture, institutions and collective preferences may lead to different but legitimate choices, without any particular system being clearly preferable to another. While the aim of fighting discrimination is easily shared, putting it into practice is far from being straightforward.