It is conceivable that the construction of a convention is in question in a case brought before ICJ and a State that is a party to the convention but not to the case has legal interests which may be affected by the construction given by the judgment in the case. As hinted at in the Whaling in the Antarctic case and the Sovereignty over Pulau Ligitan and Pulau Sipadan case, such a third State might intervene in the proceedings under Article 62 as well as Article 63 of the Statute unless it should be interpreted otherwise. In light of relevant provisions of the Statute and jurisprudence of the Court, this paper explores the question whether such a State has the choice, to submit an application to intervene under Article 62 or to make a declaration of intervention under Article 63.