This article examines the jurisdictional awards in two pending ICSID cases against Argentina-Abaclat and Ambiente-that allowed a multitude of Italian bondholders affected by Argentina's sovereign debt default to collectively use the investment treaty arbitration process, without requiring any additional or specific consent from the state.Such collective proceedings raise complex issues in relation to the state consentcentric paradigm of international investment law. The article considers the following distinct, but nevertheless interrelated, matters arising from the Abaclat and Ambiente awards, in an attempt to identify a taxonomy of collective or multi-party claims in international investment law: (i) characterisation of the nature of the proceedings; (ii) whether a host state's general consent to arbitration can be taken to include consent to being sued by multiple investors in one and the same arbitral proceeding; (iii) interpretation of the silence regarding the issue of collective proceedings in the current legal framework under the ICSID Convention; and (iv) whether collective proceedings require a certain link or relationship between the co-claimants, their respective investments and/or claims.