This study sought to test the validity of the psychological health model of Rational Emotive Behaviour Therapy (REBT). Specifically, this study sought to investigate if rational beliefs were associated with happiness and optimism. A multinational sample of 397 university students completed self-report measures of rational beliefs, happiness and optimism. Structural equation modelling (SEM) was used in order to test the validity of the REBT model of psychological health. The result of the SEM analysis provided empirical support for REBT’s psychological health model of happiness and optimism. The model as a whole explained 33% of variance in levels of happiness and 40% of variance in levels of optimism. Self-acceptance beliefs were positively and directly associated with happiness and optimism. Preference beliefs were positively and indirectly associated with happiness and optimism via self-acceptance beliefs. REBT may offer a viable psychotherapeutic method to not only alleviate psychological distress, but also build positive emotion. Current findings may help to bridge the divide between the fields of positive psychology and clinical psychology.