Legal certainty, a feature of the rule of law, constitutes a requirement for the operational necessities of market interactions. But, the compatibility of the principle of legal certainty with ideals such as liberalism and free market economy must not lead to the hastened conclusion that therefore the principle of legal certainty would be compatible and tantamount to the principle of economic efficiency. We intend to analyse the efficiency rationale of an important general principle of EU law—the principle of legal certainty. In this paper, we shall assert that not only does the EU legal certainty principle encapsulate an efficiency rationale, but most importantly, it has been interpreted by the ECJ as such. The economic perspective of the principle of legal certainty in the European context has, so far, never been adopted. Hence, we intend to fill in this gap and propose the representation of the principle of legal certainty as a principle of economic efficiency. After having deciphered the principle of legal certainty from a law and economics perspective (1), we shall delve into the jurisprudence of the ECJ so that the judicial reasoning of the Court as this reasoning proves the relevance of the proposed representation (2). Finally, we conclude in light of the findings of this paper (3).