Gratitude is one of the most neglected emotions and one of the most underestimated of the virtues. In most accounts of the emotions, it receives nary a mention. Even in broader surveys of the attitudes, it is often ignored.And in the most prominent lists of the virtues, notably Aristotle’s, it is not included. Gratitude is often included, of course, in Christian treatises on the virtues, but then it is usually directed only toward a single if exceptional object, namely God the Almighty.And yet gratitude is one of those responses that seems essential to and among civilized human beings, and perhaps it is even significant among some social animals, as de Waal and others have persuasively shown.