This article appraises effectiveness in operational conflict prevention. By focusing on the European Union Rule of Law Mission (EULEX) in Kosovo, it assesses the most extensive civilian Common Security and Defence Policy mission so far. Contrary to prevailing assessments, it posits that EULEX, despite its challenges and deficiencies, presents positive contributions to operational conflict prevention, and peacebuilding in general. This is uncovered through structured focused analysis according to effectiveness criteria and success indicators that allow for identification of and distinction between different types and levels of effectiveness, considering both means applied and ends achieved. In so doing, the article contributes to the general literature on operational conflict prevention and on the specific case of Kosovo. The empirical analysis is based on fieldwork and semi-structured interviews with EU personnel, governmental and non-governmental actors in Kosovo, and independent observers.