Atheism is a familiar kind of skepticism about religion. Moral error theory is an analogous kind of skepticism about morality, though less well known outside academic circles. Both kinds of skeptic face a "what next?" question: If we have decided that the subject matter (religion/morality) is mistaken, then what should we do with this way of talking and thinking? The natural assumption is that we should abolish the mistaken topic, just as we previously eliminated talk of, say, bodily humors and unicorns. The fictionalist, however, offers a less obvious recommendation. According to the fictionalist, engaging in the topic in question provides pragmatic benefits that do not depend on its truth-in a way roughly analogous to engaging with a novel or a movie. The religious fictionalist maintains that even if we were atheists, we should carry on talking, thinking, and acting as if religion were true. The moral fictionalist maintains a similar view regarding moral talk, thought, and action. Both forms of fictionalism face serious challenges. Some challenges can be levelled at either form of fictionalism (or at any form of fictionalism), whereas others are problems unique to moral fictionalism or to religious fictionalism. There are important questions to be asked about the relationship between these two kinds of fictionalism. Could moral fictionalism be plausible even if religious fictionalism is not (or vice versa)? This is a volume of thirteen previously unpublished papers on the topics of religious fictionalism, moral fictionalism, and the relation between these views.