This thesis reports an experimental study that examines the role of communication medium and liar motivation on deception detection. Participants were randomly assigned to one of two dyadic communication conditions, text-based instant messaging or face-to-face, and to one of two motivation conditions, high or low. Participants engaged in a discussion of four topics, in which one participant was deceptive during two topics and truthful during the other two. No main effect of communication medium or motivation level was observed. However, an interaction effect suggests that highly motivated liars interacting in an instant-messaging medium were the most successful in deceiving their partners. The implications of these results are discussed both in terms of the elimination of nonverbal cues and the potential advantages offered by text-based communication settings to the motivated liar.