Although dissents are not generally encouraged in international arbitration, they are a reality of investment treaty disputes. About one in five cases includes at least one separate or dissenting opinion. The ICSID Convention is rare among investment arbitration rules to expressly recognise the right of the arbitrator to attach his or her personal opinion to the award. Other investment arbitration rules are silent on the topic. And yet dissenting opinions are an established feature of several international courts and tribunals and their role is often viewed more benevolently than in investment arbitration. The article explores the perceived advantages and disadvantages of dissents as identified in different legal settings, including in public international courts and municipal legal systems, and critically applies them to investment arbitration. Normatively, it expects that dissents function in a broadly similar manner in investment arbitration and in other public international courts and tribunals. But it also recognises that this is nuanced by particularities of context and notably the terms of appointment of the adjudicator.