Mussar literature is older than the movement that made it famous. Bahya ibn Paquda's eleventh century Chovot HaLevavot, Duties of the Heart, argued that Jewish law governs outward action but leaves the inner life, humility, trust, sincerity, largely unaddressed, and set out to supply what the law had left silent. Moshe Chaim Luzzatto's eighteenth century Mesillat Yesharim, Path of the Just, organized the moral life as a ladder of ascending traits, each a precondition for the next, running from watchfulness up to holiness.
Rabbi Israel Salanter turned this literature into an organized movement in Lithuania in the 1840s. His central innovation was psychological rather than purely textual: he judged that intellectual assent to an ethical teaching does not by itself change behaviour, since habitual character traits, what the tradition calls middot, operate beneath conscious deliberation and resist correction by argument alone. His houses of mussar were rooms set aside for the practice he devised to reach that level, slow, emotionally engaged repetition of a single ethical text aloud, sometimes to a melancholy tune, combined with a nightly private accounting of the day's conduct against a chosen trait.
The movement split after Salanter's death over how far mussar study belonged inside the yeshiva curriculum. The Novardok approach made mussar training the centre of the school day, through deliberately unsettling exercises meant to break social convention; the Slabodka approach favoured human dignity and greatness as the ground for self improvement, shaping much of later Lithuanian yeshiva culture. Both descend from the same houses of mussar, disagreeing about method rather than about mussar's basic claim that character is trained, not simply taught.