 The negotiation of a multilateral treaty is usually a more difficult and more cumbersome process compared to the negotiation of a bilateral treaty. As more voracious speak, it becomes more complicated to find an agreement on every single point discussed. But this agreement on points of details should not prevent agreement on the core principles and rules of the new treaty. For instance, a state may like 90% of what is in a treaty, but dislike what some of its provisions provide for, provisions that are of minor importance. In such a case, it would be sad not to have that state on board of the treaty. But if the logic is take it or leave it, the risk is that such state will not consent to the treaty at all, despite the fact that it very much like most of it. So in order to encourage the conclusion of an accession to multilateral treaties, parties are often entitled to make reservation to the treaties they contract. And 2 paragraph 1D of the Vienna Convention defines the concept of reservation as follows. Reservation means a unilateral statement, however phrased or named, made by a state when signing, ratifying, accepting, approving or acceding to a treaty, whereby it purports to exclude or to modify the legal effect of certain provisions of the treaty in their application to that state. Reservations are a difficult and very technical legal issue and this introductory course will not deal with every aspect of it. But let us try to understand the gist of the matter, even if this will already require several videos. From the definition I just read out, a few elements already appear. A reservation is a unilateral statement. Reservations need not to be agreed between the contracting parties during the negotiations, they are unilateral statements of each of them. It does not matter how the reserving state calls its reservation, it can call it reservation or declaration or statement. What matters is the intent conveyed by that unilateral statement. Such intent must be either to exclude or to modify the legal effect of certain provisions of the treaty in their application to the state making that statement. This is the proper, the intrinsic legal effect that the reservation may have. Modifying the effect of a certain provision can be easily phrased. For instance, a state may declare that it does not consider itself bound by article 66 of the Vienna Convention which confers jurisdiction to the International Court of Justice for settling certain disputes about the alleged invalidity of treaties. Modifying the effect of a certain provision is sometimes more difficult to phrase. But let us imagine, for instance, a treaty by which labour by children under the age of 16 is outlawed and that a state makes a reservation providing for the possibility of having children working in the advertisement industry provided, for instance, that prior administrative authorization be given through a specific procedure. Whether it is in order to exclude or to modify the legal effect of the treaty, the reservation may only relate to certain provisions of the treaty. Reservations must be specific, they cannot be about the treaty in general. Finally, the definition of the reservation contains an important temporal element. Reservation must be made, I quote again, when signing, ratifying, accepting, approving or acceding to a treaty, which means that they cannot be made later than when the state expresses its consent to be bound by the treaty. Once you are bound by the treaty, you must perform its obligations in good faith and it is too late to declare that you do not want to be bound by one of its provisions. Any late reservation is not a reservation and produces no legal effect. Such temporal requirement is repeated in Article 19 of the Vienna Convention. Article 19 is also important because it puts other limits to the possibility of making their reservations. And this is what we are going to see in the next video.