During negotiations, parties plan an exchange that will occur in the future and that implies a high level of uncertainty, regarding both contract conditions and final outcome. In this phase, parties are requested, according to country-specific legal framework, to act in good faith. As a matter of fact, the definition of the boundaries of the good faith principle could be used as a strategic variable to understand when a form of pre-contractual liability is both necessary and efficient. Once we have analyzed the different models of pre-contractual liability in force in the main legal frameworks, our work focuses on clarifying the social function of the civil norm that introduces pre-contractual liability, given the impact on agents’ behaviour and on the level of efficiency of the negotiations. We will focus mainly on two issues. First, the failure to disclose information as a breach of the duty to act in good faith and the cases in which the introduction of a duty to disclose is efficient; secondly, the hold-up problem as a violation of the good faith principle and as opportunistic behaviour related to the level of reliance adopted by the party who hasn’t made specific investment. Our aim is to identify and to explain the reasons of the efficiency enhancement given by the introduction of a pre- contractual liability regime.