What should the Buddhist attitude be to rebirth if it is believed to be inconsistent with current science? This chapter critically engages forms of Buddhist agnosticism that adopt a position of uncertainty about rebirth but nevertheless recommend ‘behaving as if’ it were true. What does it mean to behave as if rebirth were true, and are Buddhist agnostics justified in adopting this position? This chapter engages this question in dialogue with Mark Siderits’ reductionist analysis of the Buddhist doctrine of the two truths, conventional and ultimate. Richard Hayes (1998) characterises talk of rebirth as a useful fiction. Siderits characterises talk of persons as a useful fiction and explains and justifies statements that involve it as conventionally true despite persons not featuring in our final or ultimate ontology. Does rebirth satisfy the same criteria to count as conventionally true, and does thinking of it in these terms help explain and justify what it might mean to behave as if rebirth were true? This chapter will defend a conditional yes to these questions. In the process, it will clarify what is distinctive about the traditional Buddhist approach to rebirth, provide an analysis of how the concept of rebirth might relate to practical outcomes, and address some limitations of this approach.