This chapter addresses the issue of the calculation of damages in shareholders’ claims for reflective loss. The particularities of such claims and of the nature of the investment (i.e., shares) raise intricate questions that must often be dealt with by investment tribunals. In this regard, this chapter first addresses the specificities associated with the calculation of damages in multiparty proceedings, such as in mass claims and consolidated proceedings. It also explains the methods that have been used by investment tribunals to assess the damages suffered by shareholders in investment arbitration and proposes more cooperation among courts and tribunals at the damage phase in order to reduce the risks of double recovery. This chapter also analyses an innovative means of answering risks of double recovery: the share purchase option.