Abstract The article considers the reasons why the European Court of Justice (ECJ) judges need legal concepts when they pronounce their judgments. It points out that the ECJ as a law-interpreting and an ipso facto law-making court needs legal concepts to communicate results of its interpretative and law-making enterprise. The article also shows how in the context of Article 234 EC preliminary ruling procedure legal concepts become useful tools of portraying ECJ judgments as mere products of interpretation and not as the results of subsuming the facts of the case into a legal provision. It is by means of application of legal concepts, that the ECJ judges are able to justify that they are not overstepping the mandate they have been entrusted with. In the same time the use of legal concepts enables them to engage in dialogue with national judges, who seek guidance as to the content of EC law rules, and to maintain a strong doctrine of precedent. Most importantly, however, the use of concepts promotes coherence which, the article maintains, is the primary source of Community law's authority, and thus constitutes the foundational technique of persuading the relevant audience that Community law is indeed a legal system.