Credibility refers to the objective and subjective components of the reliability of a source or message.

Traditionally, modern, credibility has two key components: trustworthiness and expertise, which both have objective and subjective components. Trustworthiness is based more on subjective factors, but can include objective measurements such as established reliability.

Expertise can be similarly subjectively perceived, but also includes relatively objective characteristics of the source or message (e.g., credentials, certification or information quality). Secondary components of credibility include source dynamism (charisma) and physical attractiveness.

Credibility online has become an important topic since the mid-1990s. This is because the web has increasingly become an information resource. The Credibility and Digital Media Project @ UCSB highlights recent and ongoing work in this area, including recent consideration of digital media, youth, and credibility.

In addition, the Persuasive Technology Lab at Stanford University has studied web credibility and proposed the principal components of online credibility and a general theory called Prominence-Interpretation Theory.