 Questions about faith have inspired centuries of philosophical and theological reflection, particularly, though by no means exclusively, as faith is understood within the Christian branch of the Abrahamic religions. What is faith? What makes faith reasonable or unreasonable, valuable or disvaluable, morally permissible or impermissible, virtuous or vicious? How does faith relate to psychological states such as belief, desire, trust, and hope? How does faith relate to action? To what extent is faith under our voluntary control? Because answers to these further questions depend on what faith is, as well as on assumptions about relevant evaluative norms and the philosophical psychology and theory of action applicable to faith, this entry focusses on the nature of faith, while also touching upon implications of various models of faith for assessments of its reasonableness and value.