The construct of mood (defined as a transient feeling state) has been shown in numerous studies to have a great effect on our daily lives. The purpose of the present study was twofold: (1) to investigate the effects of mood on psychomotor test performance, and (2) to examine the conceptualization of mood more closely. An experiment was conducted investigating the effects of positive (happy, elated) and negative (sad, depressed) mood on a newly developed Air Force selection battery. In addition, self-efficacy, perceived performance, and causal attributions were measured as potential contributors to the mood-performance relationship. Subjects consisted of Air Force Recruits at Lackland Air Force Base. Mood was manipulated by showing emotionally laden film clips before administering the test battery. The selection battery consisted of psychomotor tests, which measure reaction time and hand-eye coordination. The mood and performance model was tested through the structural equation modeling technique, LISREL. Results indicated that mood did not have an effect on any of the variables in the model. However, this null result was likely due to a relatively weak mood induction. Self-efficacy was found to predict both performance and perceived performance, and performance was found to predict perceived performance. Post-hoc analyses revealed that performance predicted mood such that subjects who performed well were in a better mood than subjects who performed poorly. What is still in question is whether mood, in turn, influences performance. The conceptualization of mood was examined by addressing the counter-intuitive theory by Watson, Clark, and Tellegen (1988) that positive and negative mood are two independent factors. This theory was examined by comparing factor structures from two different mood scales. On a more traditional scale in which only extremely worded mood items are included, positive and negative mood factors were not found to correlate. However, on a newly constructed mood scale entitled the Composite Mood Checklist (CMC), the mood factors were found to significantly correlate in a negative direction. This finding lends evidence to Spector et al.'s (1995) argument that positive and negative mood independence is an illusion created by artifactual mood scales. / Ph. D.