The United Nations Commission on International Trade Law (UNCITRAL) Working Group III (WGIII), as the main forum the reform of investor-state dispute settlement (ISDS), continues to deliberate an ambitious agenda of reform areas of high priority. Recently, the WG marked an important milestone with the adoption of the first reform instruments on the conduct of adjudicators and investment mediation. Nevertheless, the most challenging ‘building blocks’ of reform remain to be addressed, including the systemic reform proposal for a standing mechanism, which would transform the landscape of ISDS as we know it. This chapter first captures the progress of the WGIII as it stands today, focusing in particular on the first reform instruments – the Codes of Conduct for Arbitrators and Judges in International Investment Dispute Resolution, the UNCITRAL Notes on Mediation, and UNCITRAL Guidelines for Mediation in Investment Disputes. Then, it outlines the issues that remain on the agenda of the WGIII, in particular the standing investment court, appellate mechanism, the Advisory Centre and other procedural and cross-cutting issues. The chapter concludes with reflections on the overall dynamics of the WGIII and the lessons learned thus far that could contribute to the effectiveness of the deliberations ahead.