The uncertainty of today’s working environment, including prevalence of temporary employment conditions in many industries, has affected the psychological well-being of people in the workforce. Psychological well-being affects all aspects of a person’s life, including: pleasure, job satisfaction and fulfilment, and life meaning (Seligman, 2002). Previous studies have investigated how Psychological Capital (PsyCap) and Core Self-evaluations (CSE) are positively related to job satisfaction and performance, but there is little research on the relationships of PsyCap and CSE with psychological well-being (PWB). This present study explored the relationships among PsyCap, CSE, and PWB in a convenience workplace sample of 121 Australian working adults. Results revealed that both PsyCap (involving hope, optimism, resilience and self-efficacy) and CSE (involving evaluations of one’s own locus of control, self-esteem, generalised self-efficacy, and adaptive vs ‘neurotic’ behaviour) were separately positive predictors of wellbeing, consistent with previous studies. There were overlaps in concepts but both PsyCap and CSE together predicted higher levels of well-being than either alone, and CSE was found to be a partial mediator between PsyCap and well-being indicating that both elements were needed in prediction of well-being. Practical implications include that PsyCap and CSE measures can be used together in the workplace in assessment, selection, training and development to help improve the quality of health and well-being of employees. Limitations and future research directions are indicated.