Piety (pietas) is an important concept in Spinoza’s ethics, where it describes aspects of virtuous individuals, and in his political writing, where he uses it to develop his theological views. Since Spinoza’s understanding of the term is informed by its received meaning, it is important first to mention how the term was understood in his immediate context, the seventeenth-century Dutch intellectual scene. The term would have been known foremost from the humanistic tradition, which focused on ancient Roman writers like Cicero and Tacitus, rather than from the scholastic tradition. In the classical Latin used by Roman writers, pietas refers to upright conduct, particularly dutiful conduct, but also kindness and loyalty. The term is ambiguous between upright conduct that is religious or moral in nature. In the Christian era, pietas came to refer more exclusively to the religious virtue of dutiful reverence for God. Pietas was also an important concept in Calvinist theology, the orthodox theology of the Dutch Republic.