The present work focuses on the determination of the “lawful and unlawful” from the perspective of Competition Law that is crucial for economic development. On this occasion, our examination will be limited to a simple approximation, since it is a broad and especially complex issue, which also forces us to focus on one of the various fields of Competition Law, that of agreements or collusive practices. It is, however, an essential issue, as economic operators must know the border that defines the legality or not of their performance in the markets when they maintain contacts with other companies, whether or not they are competitors, even sharing with them the participation in associations and institutions that represent them; and this is not, in many cases, easy or possible to always specify absolutely in terms of legal certainty, especially in markets and with business models in continuous creative evolution.