因信称义（拉丁语：Sola fide，天主教译作因信成义，或称作惟独信仰、惟独因信称义），为路德教会和其他认同16世纪宗教改革的教会之信仰核心思想，“因信”意为凭借「信心」，“称义”意为「人被上帝判为无罪」。这个基本教条，教导罪人单单藉上帝所赐的信心信靠耶稣基督而得救，是完全出于上帝恩典（by grace alone through faith alone），而不是出于人的善功、行为，这有别于罗马天主教与东正教认为人要蒙恩得救除信心外亦必须加上足够的善功（“补赎”）之教义。

Sola fide (Latin: by faith alone), also historically known as the doctrine of justification by faith alone, is a Christian theological doctrine that distinguishes most Protestant denominations from Catholicism, Orthodox Christianity, and some in the Restoration Movement.