The essays in this book defend evidentialism. This is the view that whether a person is epistemically justified in believing a proposition is determined entirely by the person's evidence. Fundamentally, it is a supervenience thesis according to which facts about whether or not a person is epistemically justified in believing a proposition supervene on facts describing the evidence that person has. According to evidentialism, epistemic evaluations are distinct from moral and prudential evaluations of believing, and epistemically justified beliefs may fail to be morally or prudentially valuable. The evidence to which the theory refers includes other justified beliefs and, ultimately, experiences. While evidentialism is not an inherently anti-skeptical view, we argue that people do have knowledge level justification for many beliefs. Several essays in the volume criticize rival theories of justification, notably externalist theories such as reliabilism.