Chapter 2 examines the professional ethics that guide EU legal advisers. It seeks to uncover what counts as good lawyerly behaviour in their activities. Building on interviews with sixty-three legal advisers and people who work with them, it examines the EU legal advisers’ own understanding of their work ethics. While EU legal advisers, as a rule, are not formally bound by any particular professional rules or obligations regulating their legal functions, they seem to possess a strong understanding of what counts as good and ethical conduct. Though not enshrined in a set of rules, a fairly uniform collective professional ethos appears to have developed, born out of many years of professional discourse and peer scrutiny among EU legal advisers. In the interviews, protecting the integrity of EU law features prominently and comes across as a key element in their professional ethics. Yet this is not an external and absolute concept. For EU lawyers, Union law is not immutable but a living organism. How the Treaties are interpreted can and will evolve. Protecting the integrity of EU law is not about resisting change but nurturing it in a manner that maintains the credibility and relevance of legal advisers themselves.