Understanding what they are, how they are signed and what effects they have on Spanish law is not just of academic interest: it is key for companies that operate in several countries, for investors, for expatriates or for anyone who may be affected by international standards on human rights, trade or taxation.
What is an international treaty?
The classic definition is found in the Vienna Convention on the Law of Treaties of 1969 , to which Spain adhered.
This Convention defines a 'treaty' as an international agreement concluded in writing between States and governed by international law.
The Vienna Convention also enshrines the great principle of the matter: pacta sunt servanda.
In other words, validly concluded treaties must be fulfilled in good faith by the parties that have accepted them.
Although each treaty has its own history, the basic outline is quite similar:
- Negotiation. Governments appoint negotiators and technical teams. In Spain, coordination is the responsibility of the Ministry of Foreign Affairs, without prejudice to the sectoral ministries involved.
- Text adoption and authentication. Once the content is finalized, the text is adopted and authenticated (for example, by the signature of plenipotentiaries), in accordance with the rules set out in the Vienna Convention and in the treaty itself.
- Firm. The signature may have more political than legal value; it expresses the State's will to move forward, but, unless the treaty provides otherwise, is not sufficient on its own to make the treaty fully bindingA further step will usually be necessary: ratification.
In Spain, this entire process is now systematized in Law 25/2014, on Treaties and other International Agreements , which regulates who negotiates, who can sign and how each instrument is processed internally.
The constitutional filter: authorization by the Cortes and ratification
The Spanish Constitution of 1978 reserves a central role for the Cortes Generales (Parliament) in matters of treaties. Several key provisions govern this control:
- El Article 93 allows, through organic Law, authorize treaties that attribute to international organizations the exercise of powers derived from the Constitution (for example, integration into the European Union).
- El Article 94 requires prior authorization from the Cortes Generales for certain particularly sensitive treaties: of a political or military nature, affecting territorial integrity, fundamental rights, implying financial obligations for the Public Treasury or requiring the modification of laws or the approval of new legislation.
- El Article 95 It prevents the celebration of treaties contrary to the Constitution, unless the Constitution is reformed beforehand, and the Constitutional Court may be asked to assess this possible contradiction.
Law 25/2014 outlines the procedure: the Government negotiates, the Council of Ministers decides how to express Spain's consent, and, when necessary, submits the text to the Congress and the Senate for their authorization. The Rules of Procedure of the Congress specify the deadlines and the form of this authorization.
Only when this parliamentary filter has been passed is the State in a position to complete the international process with ratification , which in Spain takes the form of an instrument signed by the King at the proposal of the Government.
When does the treaty apply within Spain?
At the international level, the treaty enters into force on the date and under the conditions it itself establishes. However, for its provisions to be enforceable within the Spanish State, an additional step is required: official publication.
Article 96 of the Constitution is unequivocal: validly concluded treaties “once officially published in Spain, shall form part of the domestic legal system .” Only in this way do they become law applicable by judges and authorities.
Law 25/2014 details this requirement: publication is made in the Official State Gazette , generally accompanied by the full text and, where appropriate, by the reservations or interpretative declarations made by Spain.
From that moment on, the treaty becomes part of the existing laws, regulations, and other internal rules. And it doesn't do so as just any ordinary guest.
What happens if a law contradicts an international treaty?
Spanish law recognizes a reinforced position for treaties.
The Constitution establishes that they can only be “modified, repealed or suspended” in the manner provided for in the treaty itself or in accordance with the general rules of international law, and not simply by means of a subsequent law.
The established doctrine and practice are based on two ideas:
- The treaty It is placed above ordinary lawIf a subsequent domestic law conflicts with a valid and published treaty, the bodies applying the law must give precedence to the treaty.
- Above all else remains the Constitution: a treaty contrary to it cannot be perfected without prior constitutional reform (art. 95 CE).
In practice, this obliges the legislator to adapt the laws to the international commitments assumed by Spain and allows the courts to use the treaties as a control parameter.
The internal framework: of Law 25/2014
Alongside the Constitution and the Vienna Convention, the other major pillar is Law 25/2014 , which for the first time offered a systematic framework on international treaties and agreements in Spain.
It regulated not only "classic" treaties, but also: administrative agreements, non-normative agreements and the participation of autonomous communities in the execution of treaties in matters within their competence.
This regulatory framework is complemented by the Regulations of Congress and by the jurisprudence of the Constitutional Court, which has specified, among other things, how the autonomous communities can intervene in the execution of treaties when they affect their powers.
How do treaties actually bind states?
Once a State has validly expressed its consent to be bound (usually by ratification) and the treaty is in force, the principle pacta sunt servanda comes into play : the State must comply with the treaty in good faith.
This means, among other things:
- Adjust their legislation and administrative practice to the provisions of the treaty.
- Refrain from taking actions that frustrate the object and purpose of the treaty.
- Respond internationally in case of non-compliance, with possible claims from other States, liability, countermeasures or even sanctions within the framework of international organizations.
In the case of Spain, moreover, Article 93 CE expressly entrusts to the Cortes Generales or the Government , as the case may be, the guarantee of compliance with these treaties and with the resolutions issued by international or supranational bodies to which powers have been ceded.
A chain of legal security between the international and the domestic
International treaties are not mere diplomatic gestures; they are legal norms with their own force , born from a complex process that combines political negotiation, parliamentary control, constitutional verification, and international formalities.
In Spain, the Constitution , Law 25/2014 and the Rules of Procedure of Congress create a system in which:
- The Government negotiates and signs.
- The Courts authorize when the content requires it.
- The King ratifies.
- The BOE incorporates the treaty into the legal system.
- Courts and administrations apply it in preference to incompatible ordinary laws.
For companies that enter into international contracts, for citizens affected by double taxation agreements, extradition treaties, or human rights treaties, understanding this mechanism is essential; there is an international treaty that, once ratified and published, is not just a political commitment: it is current law.
