The evolution of the multilateral trading system, and the creation of the W
orld Trade Organization, has heightened calls by non-governmental organizat
ions to participate in decisions about trade policy including in WTO disput
e settlement as amicus curiae; or 'friends of the court'. Amicus briefs hav
e now been received by a number of WTO panels and the Appeillate Body, rais
ing an outcry from many WTO Members, and calls by others for the creation o
f criteria to guide their use. This note explores the practical implication
s of amicus briefs, and suggests criteria for their use in light of current
WTO practice, the goals of the WTO and its dispute settlement mechanism, a
nd the practice of other international courts and tribunals. It commences b
y examining the main WTO disputes in which amicus briefs have been received
, and the varying responses of WTO adjudicating bodies. It then examines th
e approach of other international fora - including the International. Court
of Justice, the human rights tribunals, and the International Tribunal for
the Law of the Sea - to involvement of non-parties. Drawing on these exper
iences, it suggests that WTO panels and the Appellate Body should weigh bot
h substantive criteria (relating, for example, to the character of the amic
i, the nature of its submission, and the characteristics of the case) and p
rocedural criteria (relating to issues such as timing and format) when dete
rmining whether, and if so, how to use amicus briefs. The note also identif
ies the mechanisms that may be used to establish criteria to ensure amicus
briefs promote predicability and procedural fairness in WTO dispute settlem
ent.