The Apostille Convention is an international convention. It is created by the Hague Conference on Private International Law. This convention specifies the formalities through which a document issued in one of the signatory countries. In addition it can be certified for legal purposes in all the other signatory countries.
It is an international certification comparable to a notarization in domestic law. Normally supplements a local notarization of the document. In other words if the convention applies between two countries, such an apostille is sufficient to certify the document’s validity. Because of that, it removes the need for double certification by the originating country and then by the receiving country.