All people want to be happy. This is a principle that has been widely accepted since Plato and Aristotle up to the 18th century in eudaimonistic ethics, which is focused on happiness, and which Thomas Aquinas also adheres to. But what is happiness? What is necessary for happiness? What makes a person happy, and how can happiness be achieved? And is it the ultimate goal for every person? These are the questions that Thomas discusses in detail in the five Quaestiones (sections) of his treatise on happiness in the Summa Theologiae, providing answers that can still impress and offer guidance today. The goal does not lie in the accumulation and provision of individually gratifying goods, but in the self-realization of the person in the sense of the complete unfolding of their nature and essence.