Both legalisation and the Hague Apostille confirm the authenticity of the signature and the authority of the issuer of the document. In the case of legalisation, this is done by the consular officer of the state in which the document is to be used.  In the case of the Hague Apostille, on the other hand, this is done by the corresponding authority of the state by which the document was issued.  Mutual legalisation is often no longer necessary due to international treaties and is replaced by the Hague Apostille.