This Element provides an account of Thomas Aquinas's moral philosophy that emphasizes the intrinsic connection between happiness and the human good, human virtue, and the precepts of practical reason. Human beings by nature have an end to which they are directed and concerning which they do not deliberate, namely happiness. Humans achieve this end by performing good human acts, which are produced by the intellect and the will, and perfected by the relevant virtues. These virtuous acts require that the agent grasps the relevant moral principles and uses them in particular cases.