One of the topics covered in the Law against Unfair Competition is the application of the prohibition of unfair competition to practices consisting of the exploitation of products, services and distinctive signs protectable by industrial property rights, both in cases where they have not been protected and in those where they are in fact protected at the time the challenged practice is carried out, or where they were protected in the past. Case law has addressed this matter in accordance with the so-called “principle of relative complementarity,” initially proposed by a segment of the Scholars. This paper is dedicated to studying the legal basis of this principle, its formulation, its implications and limits, as well as the most notable groups of cases.