First things first, an apostille doesn’t validate the contents of a document. Instead, it is simply attached to
verify that your documents are legitimate and authentic.
Before 1961, the burden of judging the authenticity of documents rested on foreign courts and authorities. If,
for example, you were travelling from the U.S. to the U.K., you would need to land in the U.K. and then get
their authorities to verify the authenticity of your documents.
However, on October 5th, 1961, The Hague Convention abolished that system and introduced a new one
where documents are verified in the country of origin. Upon verification, the traveler is given a certificate
called an apostille.
Thus, an apostille is recognized and accepted by all the member countries of the Hague Convention, which the U.S. joined in 1981. It doesn’t just certify documents, but it also abolishes the requirement of diplomatic or consular legalization of public documents in a foreign country.
It's worth mentioning that apostilles are only issued for documents that are meant to be used in a foreign
country (that’s a member of the Hague Convention). You don’t need an apostille to travel within U.S.
jurisdictions like Guam, Puerto Rico and the Virgin Islands.