This chapter will examine the validity of choice of court agreements in international commercial contracts under the Hague Choice of Court Convention and the EU’s Brussels Ia Regulation. It will be argued that the significant lessons learnt from the jurisprudence on choice of court agreements under the Brussels Ia Regulation and its predecessor instruments should not be ignored. Unlike the CJEU’s early and restrictive jurisprudence on the writing requirement, Article 3(c) of the Hague Convention should be broadly interpreted. The independent concept of consent distinct from the substantive validity of a choice of court agreement developed under Article 25 of the Brussels Ia Regulation should also be applied in the context of the Hague Convention. This autonomous and wide concept of consent will reduce the need to rely on the choice of law rule governing the substantive validity of choice of court agreements, which refers to the law of the chosen forum including its private international law rules. It will be observed that the unilateral national choice of law rules of the Member States and Contracting States may act as an impediment to the sound operation of the choice of law rule by creating uncertainty and risking decisional harmony.