Legalization is the process through which an official document is authenticated and certified to be used internationally. Thanks to the legalization process, documents will be accepted by a foreign country different from the one where documents were released.
The Apostille was established by the Hague Convention Abolishing the Requirement for Legalisation for Foreign Public Documents, or Apostille Convention, drafted by the Hague Conference on Private International Law on October 5, 1961. The treaty outlines the modalities through which a document issued in one of the signatory countries can be certified for legal purposes reducing the authentication process to a single formality: the issuance of the Apostille.
If the country where you need to use your documents is not a member of the Apostille Treaty of the Hague Convention, you will need a consular legalization. Before obtaining a consular legalization, documents should be prior authenticated by an Italian competent authority.
img : Apostille Section @ http://www.hcch.net/