This article discusses the Hebrew term musar, which is commonly translated as “Jewish ethics,” with particular reference to the early modern context. It provides an overview of the linguistic use of the term from biblical literature to the pietistic-philosophical writings of the Middle Ages and from early modern attempts to classify a corpus of musar to contemporary scholarly reflections on the implications of the concept. It shows how the term and its cognates derived from the root ysr were used to denote disciplinary measures or rebukes by parents, fellow human beings or a divine power, as well as voluntary acts of self-disciplining or self-mortifications, and how its connotation changed under the influence of Sufi thought towards the description of a neo-platonically inspired inner spiritual refinement with the aim of approaching the divine. Furthermore, it discusses how (early) modern attempts to systematize this literature either described its characteristics by using emic terminology from the sources themselves (such as “fear of God” or “divine love”), or presented musar within the framework of a universal ethics, distinguishing it from halakha [religious legal obligations]. Drawing on contemporary scholarly discourses, the essay touches on the hypernomian and gendered dimensions of musar, as well as the proposal to view these highly diverse literary expressions as a literary mode (or modes) rather than a genre. The article introduces some of the key features of musar writings. In doing so, it addresses how musar served as a tool for disseminating esoteric knowledge, and for defining and maintaining power relations related to communal structures and gender.