The primary aim of this research was to examine the influence of temporary mood states on factual and interpersonal skepticism. Based on recent affect-cognition theorising and research on credibility judgment, 7 studies predicted that negative moods increase and positive moods decrease skepticism, because of the information-processing consequences of these affective states. First, three studies examined the influence of mood on factual skepticism toward urban myths and legends (Study 1) and novel and familiar general knowledge claims (Studies 2-3). Contrary to predictions, Study 1 found that sad participants were less skeptical than happy participants towards urban legends, possibly due to the negative valence of the claims. Because the feeling of familiarity has been shown to be an important determinant of truth, Studies 2-3 examined the influence of mood and familiarity on skepticism. Consistent with information processing theories of mood, happy participants were more likely than sad participants to give credence to familiar general knowledge claims (Study 2), even when given explicit feedback about their actual truth or falsity during initial exposure to claims (Study 3). The remainder of this thesis extended these findings to interpersonal judgments. Studies 4-5 found that sad participants were more skeptical of the genuineness of facial expressions of emotion compared to happy participants. Studies 6-7 examined whether sad participants might also show greater lie detection accuracy. In Study 6, happy, sad and neutral-mood participants judged the credibility of targets honestly or deceptively describing their emotional reaction to an affectively-laden film, but no evidence was found of mood induced differences in deception detection accuracy. However, in Study 7, sad participants were more skeptical than happy participants about the veracity of videotaped individuals honestly or deceptively denying their involvement in a mock crime (a theft), and showed greater accuracy at discerning lies from truths. This dissertation contributes to the affect-cognition literature by demonstrating that not only may sad moods lead people to be more skeptical, but they may also confer an advantage at detecting deception. The implications of these findings for everyday credibility judgment and for contemporary theories of affect and cognition are considered.