Two studies were conducted in the research domain of Health Psychology to investigate factors influencing undergraduates' engagement in unprotected sex. Specifically, associations were investigated between socio-cognitive factors (attitudes, norms), culture (British versus Greek) temporal factors (having a present or future time perspective - TP), and contextual factors (relationship status - RS) and intended and actual non-condom use. The influence of past non-condom use was also examined. Additionally, the adequacy of socio-cognitive theories typically used in risk research, such as the theories of reasoned action (TRA) and planned behaviour (TPB), was assessed. A total of 342 students participated (112 in Study 1 and 230 in Study 2). A mixed-methods sequential design was employed, encompassing quantitative and qualitative techniques. Results showed that: past non-condom use revealed the strongest relationship with intended unprotected sex, followed by attitudes, relationship status, and fatalistic time perspective. The TRA variables were sufficient predictors of intended unprotected sex, with perceived behavioural control not being a substantial addition, thus, TPB was not established superior. Past unprotected sex, present-fatalistic TP, RS, and culture were significant predictors of intended unprotected sex. Past behaviour was the strongest predictor of non-condom use for participants in exclusive relationships, whereas, attitudes were the strongest predictors of unprotected sex for single participants. Thus, it was argued that interventions aiming at changing young peoples' attitudes towards enhancing condom use should target partners in exclusive relationships. Finally, cultural differences were found regarding preference in contraceptive methods and serial monogamy. To conclude, this research demonstrated the necessity of combining cognitive, habitual, contextual, and ethnic factors whilst studying sexual risk. Predominant theoretical models emphasizing rationality in sex-related research may be re-assessed, on the basis of this study's results. Also, the effectiveness of employing mixedmethodologies was established.