Lobbying on both sides of the Atlantic has experienced a considerable boom in the last 50 years and one could be led to believe that the two industries look increasingly alike. Lobbyists have become highly professionalized and master a multitude of venues and levels of political authority. Direct representation of companies or other stakeholders co-exists with associational representation in both Washington DC and Brussels, even though peak associations play a greater role in Europe. The use of some instruments is different, however, in particular financial contributions and legal tactics, which are central in the United States (US) and much less common in the European Union (EU). What is more, observers of lobbying in the US and the EU have noted the markedly different lobbying styles: frequently aggressive advocacy approach in the US and a more consensus-oriented informational lobbying in the EU. While US groups and lobbyists oftentimes defend their immediate interest by trying to exert pressure on public officials, EU representatives seem to be more soft-spoken in their approach and are said to work in a more constructive manner with bureaucratic and political representatives. After developing a description of what makes up the respective styles, this article discusses cultural and institutional explanations cited in the literature. Rather than seeing lobbying styles as culture traits, it discusses the institutional constraints affecting lobbying behavior. In particular, the passage rate of proposals, the fragmentation of public media, the electoral structure and the transparency of political negotiations create different incentive structures in the US and the EU. However, lobbying styles are more than the cumulative effect of these different elements. They are linked to the nature of the political system, of which the institutional constraints are a reflection. The US, a fully established federal system, relies on majority decision-making. This creates an adversarial culture and ‘winner-takes-all-politics’. The EU, by contrast, functions as a complex inter-governmental system with a high degree of supranational centralization. The resulting tension between integration and inter-state bargaining creates a system that relies on consensus-building. In this context, the access of private actors to supranational institutions depends on their contribution to the creation of problem-solving policy approaches. As long as the EU has to rely on the acceptance of its policy outputs for its legitimacy, we are bound to find many individual mechanisms that will trigger a more soft-spoken lobbying style in the EU. The differences between the US and the EU styles will thus appear as instances of a particular political culture, even though they are based on a range of institutional mechanisms, which are in turn a consequence of the construction of the respective political system. In conclusion, the article discusses the implications of this distinction for understanding change over time.