The procedure by which the signature and seal of a public official of one country (such as a notary public) is authenticated by a competent authority of a different country (usually a consular officer). For example, a court in Brazil may require an affidavit sworn before a US notary to be legalized by a Brazilian consular officer before the affidavit can be used in a Brazilian lawsuit.

Legalization is not required if both the originating country (that is, the country where the document was signed and notarized) and the destination country (that is, the country where the document is to be used) have ratified the 1961 Hague Convention Abolishing the Requirement of Legalization for Foreign Public Documents (Hague Apostille Convention). Under the Hague Apostille Convention, signatory countries have agreed to recognize public documents, including notarial certificates, issued by other signatory countries if those documents contain an apostille issued by the originating country's competent authority (such as a Secretary of State). The US ratified the Hague Apostille Convention in 1981.