Specific procedures for third-parties joinder in arbitration rules are now included in most institutional rules, and stands out as a key recent development in arbitration procedure. This development highlights the system’s responsiveness and versatility in addressing users’ new needs to respond to the changes in business practice, which has become more complex and involved more parties and transactions.

The chapter provides an overview and assessment of the most frequently used rules, in both commercial and investment arbitration, including under the ICC, LCIA, CIETAC, SIAC, HKIAC and UNCITRAL, in relation to third-parties joinder. These rules have addressed in a variety of ways the central issue of consent of the parties to arbitration, which is a key foundation of international arbitration.

Moreover, the rules have also sought to continue to implement the principles of equality and neutrality, which are fundamental to arbitration and key reasons why parties select to go to arbitration in the first place. Thus, while addressing demands for flexibility and reconfiguration of a bi-lateral into a more multi-lateral system, the rules have also tackled and resolved appropriately the key problem of providing the parties with an equitable way to appoint arbitrators of their own choosing.