In international arbitration, there is an intrinsic tension between the autonomy of arbitral institutions and that autonomy of the parties. This tension is caused by the increasing role played by arbitral institutions, both with respect to the quasi–normative force of their rules and their enhanced decisional powers in the implementation of these rules. In light of the vast authority granted to some arbitral institutions, the quality of institutional administrative decision–making is sometimes even closely linked to the person holding the relevant office. Due to the potentially harmful effect on party autonomy, modern institutional arbitration is regarded by some as not entirely in keeping with the principle of the primacy of the parties’ intentions. Others even see the interventionist attitude of some arbitral institutions as an additional ground for legitimacy concerns which are being raised with respect to the international arbitral system as a whole. Where the arbitration rules grant the institution discretion to decide matters concerning the administration of the proceedings, party agreements should, as a rule, trump the discretion of the institution. This approach serves to avoid potential damage to both the attractiveness and the legitimacy of institutional arbitration inflicted by the party autonomy paradox.