The contributions of Albert Ellis to the understanding of human happiness including his suggestions for living a happier life have not been represented in the field of positive psychology. This article presents Ellis? theoretical constructs associated with his conception of happiness (dual nature of human psyche self-actualization purpose and goals of life and short- and long-term happiness). Eleven of Ellis? rational principles of living (e.g. self-interest self-direction self-acceptance commitment to absorbing activities hedonism) are presented. When consistently applied in practice they may help people to experience frequent positive affect less frequent and intense negative emotions and high life satisfaction. It will show how Ellis? ABC-DE scientific method can be used with individuals to lessen unhappiness. Suggestions are provided for research into associations between rationality and happiness as well as the impact of different rationality-based interventions on happiness.