At 38,000, the total number of staff at the European Commission is relatively small for a body representing half a billion citizens. Likewise, the 3,500 strong research and statistical team is modest in size given that it operates across the Directorates General and other services. In order to assist policy-makers, the Commission supplements this research base by using outside expertise to advise at all stages of the policy-making process. For many years, those who observe the European Union’s institutions have recognised that this use of outside expertise to assist with the shaping of policy presents a potential democratic shortfall. The 2001 White Paper on Governance acknowledged that the line between expertise and political authority had become blurred and that, increasingly, the public questioned the independence of expert advice. The following year, the Commission published its first set of guidelines on the collection and use of expertise, listing ‘openness’ as one of three core principles. Despite considerable changes that have occurred in the transparency landscape in the intervening period, the Commission’s commitment to this core principle of expertise remains. This article investigates the measures the Commission introduced specifically to facilitate this openness. Applying a structure-agency approach, the article characterises an expert group as a ‘community of knowledge’ and contrasts the transparency of the Commission’s formal appointment procedures with the less visible but frequently used informal measures through which individuals are identified and approached. Based on a recent and highly relevant case, the article employs data gathered from the near contemporaneous accounts of expert group members and Commission officials. It finds that the reported appointment processes do not reflect the widespread incidence of individuals selected based on previous contact or personal recommendation and argues that this may undermine the integrity of the Commission’s core principle of openness in the use of expertise and in its broader transparency measures. In terms of the motivation of those responding to the Commission’s call for experts, the article finds that membership of an expert group confers a degree of professional prestige that directly benefits individual members and offers competitive advantage to their parent organisations.