Moral sense theory (also known as moral sentimentalism) is a theory in moral epistemology and meta-ethics concerning the discovery of moral truths. Moral sense theory typically holds that distinctions between morality and immorality are discovered by emotional responses to experience. Some take it to be primarily a view about the nature of moral facts or moral beliefs (a primarily metaphysical view)—this form of the view more often goes by the name "sentimentalism". Others take the view to be primarily about the nature of justifying moral beliefs (a primarily epistemological view)—this form of the view more often goes by the name "moral sense theory". However, some theorists take the view to be one which claims that both moral facts and how one comes to be justified in believing them are necessarily bound up with human emotions.

Popular historical advocates of some version of the moral sense theory or sentimentalism include the 3rd Earl of Shaftesbury (1671–1713), Francis Hutcheson (1694–1746), David Hume (1711–1776), and Adam Smith (1723–1790). Some contemporary advocates include Michael Slote, Justin D'Arms, Daniel Jacobson, Jesse Prinz, Jonathan Haidt, and perhaps John McDowell. Simon Blackburn and Allan Gibbard endorse a non-cognitivist form of sentimentalism.