The Holy Grail of ICSID Arbitration is social justice. Amicus Curiae is the Grail Castle that holds the sacred chalice of ICSID’s salvation. This paper comments on both the procedural and substantive law of amicus curiae submissions in Investor-State arbitrations. Issues of human rights and public interest that arise in these disputes must be addressed through an increase of amicus submissions whilst still protecting provisions for confidentiality. Only by identifying matters that are highly relevant to the public interest that normally would not be addressed (either in the dispute or elsewhere) can amicus curiae be used. It is incumbent upon arbitration tribunals to allow these issues to be raised in connection to the dispute so that the procedural and substantive requirements to file leave for amicus curiae can be undertaken. The principle of amicus curiae serves as the foundation for social justice in ICSID arbitrations.