Pact of contrahendo, mainly mentioned under the Latinism or Latin phrase pactum de contrahendo, is a legal term originating in the field of Roman Law, which refers to a pre-contract or preliminary agreement in which two or more parties undertake to negotiate a future contract or formal agreement on some specific matter. So this pre-contract would have been allowed, but originally subject to the same procedural requirements that should govern the final contract to which it should give rise.[2]​ Even so, there are authors who, despite recognizing the Roman origin of the expression and the existence of pre-contractual figures and the respective casuistic examples in that civilization, deny that Roman Law has reached the level of abstraction necessary to develop a kind of theory in this regard.[3]​.

This in general, since the precise scope of the expression pactum de contrahendo can vary and be qualified according to the criteria of various authors, sources, jurisdictions and matters of law in which it is applied, differing in some aspects from other pre-contractual forms, such as the similar pactum de negotiando").

Regarding International Law, for example, the Encyclopaedic Dictionary of International Law ("Encyclopedic Dictionary of International Law") edited by the University of Oxford, starts by pointing out in the respective entry that the "exact meaning (of pactum de contrahendo) is uncertain", adding that "fortunately (the phrase) is rarely used".[4]​.

Despite this statement, there have been various cases in which the concept has been the focus of international affairs and litigation. For example, in May 2015 the concept had special importance in the jurisdictional allegations made at the International Court of Justice in The Hague, following the lawsuit filed before that court by Bolivia requesting that Chile be imposed with the obligation to negotiate "sovereign access to the sea." On that occasion, the Plurinational State of Bolivia focused an important part of its presentation on arguing the supposed existence of a pactum de contrahendo in that sense between both states.[5]​.