An altruistic wager is a type of argument that seeks to establish that an agent should act as though a conclusion is true because, given what we know, that seems to be the right decision from an ethical perspective, even if the conclusion does not actually seem likely to be true. For example, one might argue that one should act as though animals are sentient and are moral patients when deciding whether to be a vegetarian, as long as that has any nontrivial chance of being true, because if it is true the ethical harms of eating meat might very much outweigh the ethical or self-interested benefits. 

Altruistic wagers often assume an agent should behave according to expected value theory, but some such wagers may also hold under some alternatives to expected value theory. Some wagers may even hold more strongly under particular alternatives to expected value theory, such as a theory that incorporates risk-aversion.