In 1961, many countries joined together to create a simplified method of authenticating documents for universal recognition. Members of this conference, referred to as the Hague Convention, adopted a document referred to as an Apostille that would be recognized by all member countries (including Spain).
There are two categories of destination countries: those that are part of the Hague Convention and those that are not. Apostilles can exclusively be obtained for countries within the Hague Convention. If your intended destination falls outside the scope of the Convention, it is categorized as a non-Hague Country. In such cases, authentication is required through the U.S. Department of State/Department of Justice in Washington D.C. and/or full embassy legalization for that specific country.