In this Compendium we have encouraged the authors to address both commercial and investment arbitration through the lens of their respective topics. This contribution highlights those areas in which investment arbitration has no or very little analogue with commercial arbitration. It sets out the incontrovertible fact that the state’s presence has certain ramifications.Investment treaty arbitration is ‘arbitration without privity’, in which a state has given its consent in advance to arbitrate a dispute submitted by an unknown (but defined) class of persons about an unknown (but defined) type of claim arising from an unknown (but defined) project. These uncertainties mean that objections to the jurisdiction and admissibility of claims are frequent, indeed almost de rigueur.The notion of applicable law in investment arbitration is complex, involving intersections between public international law and municipal law, between different public international law regimes, and even scrutiny as to whether investment tribunals can themselves develop law.State immunity can hinder the execution of awards. Because of the public interest in arbitral awards, transparency has come to be regarded (at least theoretically) as an essential attribute of investment arbitration. This chapter offers a smorgasbord of some of the most notable particularities of investment arbitration.