Sola fide (by faith alone) is the doctrine held by some Protestant denominations of Christianity but rejected by other Christians that only through faith alone is salvation possible.
The doctrine was first stated by Martin Luther, and as such is an outcome of the Protestant Reformation. The doctrine was put forth to oppose the idea that works or good deeds play a role in our salvation as well. Because the Book of James emphasizes the importance of good works, Martin Luther sometimes referred to it as the "epistle of straw".
See also: sola scriptura