During negotiations, parties plan an exchange that will occur in the future, and that consequently produces a high level of uncertainty regarding both contract conditions and the final outcome. During this phase, parties are requested to act in good faith, so good faith could be used as the parameter to understand when a form of pre-contractual liability is necessary, and which is the efficient level of liability. Once analyzed the different models of pre-contractual liability, the aim of our work is to clarify the social function which responds to the civilistic norm that introduces pre-contractual liability, given the induced effect on agents behavior and the consequences that it determines on the efficiency of the exchanges. We will focus mainly on two issues: the missed disclosure of information as a breach of the duty to act in good faith and the cases in which the introduction of a duty to disclosure is efficient; the hold-up problem as a violation of the good faith principle and as a opportunistic behavior 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 due to the introduction of a pre-contractual liability regime in these cases.