Excessive sedentary behavior is associated with negative health-related outcomes. University students have been identified as a highly sedentary segment of the adult population. Understanding psychological factors that influence sedentary behavior in university students is critical for informing interventions. Social cognitive theory (SCT) offers a framework to explore cognitive and motivational factors that may influence sedentary behavior. Using SCT as a framework, this thesis explored university students’ knowledge, self-efficacy, and outcome expectations related to reducing sedentary behavior and examined the effects of a self-affirmation intervention on students’ processing of and social cognitive reactions to health risk information related to sedentary behavior. Study 1 found that while some students understood the concept, some did not fully understand the concept. Most students were knowledgeable about health risks associated with sedentary behavior. Students’ self-efficacy (task, context-specific) and outcome expectation beliefs related to reducing sedentary behavior were not associated with their actual sedentary behavior. Self-regulatory efficacy, however, emerged as an individual social cognitive correlate of sedentary behavior. Study 2 employed a qualitative approach (focus groups) to explore the same topics investigated in Study 1, including barriers and ideas related to reducing sedentary behavior. Three themes were identified: (1) conceptual confusion, but knowledgeable about risks, (2) confident, but unlikely to change, and (3) ideas and recommendations. Study 2 determined that some students found health risk information pertaining to sedentary behavior to be threatening. This finding informed Study 3, the aim of which was to test whether a self-affirmation intervention could improve students’ processing of and reactions to health risk information on sedentary behavior and elevate self-efficacy and outcome expectations related to reducing sedentary behavior. Self-affirmation appeared to have had no effect on measures of message acceptance, derogation, risk perceptions, negative affect, intentions, self-efficacy, or outcome expectations. Speculatively, the null effects of self-affirmation were because students may not have found health risk information related to sedentary behavior to be threatening to their self-integrity – a condition considered necessary for self-affirmation to yield benefits. Collectively, findings presented in this thesis advance knowledge of university students’ perceptions of sedentary behavior and factors that influence students’ decisions to be less sedentary.