Regulatory Impact Assessment (RIA) is a method of public policy analysis that has been gaining more and more significance in the regulatory systems in the United States and the European Union. The method, developed in the 1980s in the United States, is currently applied by government institutions in a number of developed countries throughout the world, for example the Member States of the European Union. RIA is a document pointing out the potential costs and benefits of a draft regulation. It is drawn up using quantitative and qualitative analysis, which indicates the regulations that bring more benefits to the society than costs and therefore makes it possible to assess whether it is profitable to implement the regulation. This article presents the evolution of the approach to RIA in the European Union and the United States by comparing the two models and applying the research method of historical/institutional analysis. The issue is discussed in the context of the transatlantic cooperation between Brussels and Washington on the reform of regulations and development of trade and investment cooperation under the negotiation of the Transatlantic Trade and Investment Partnership (TTIP). Furthermore, the article identifies the differences in the approach to RIA on the two continents as well as the possible areas of cooperation in the area of regulation.