 What would it mean to say that a petitionary prayer to God had been answered? Petitionary prayers often make many differences to those who offer them, whether positive or negative (see Phillips 1981 and Brümmer 2008), but the more philosophically interesting question is whether or not such prayers make a difference to God. And the question is not whether God simply hears or notices such prayers—after all, we have assumed that God knows everything that happens in the world and is perfectly good. Typically, when philosophers discuss the effectiveness of petitionary prayer, they wonder whether petitionary prayers ever move God to act in some way. What would it mean to say this?