Mesillat Yesharim or Mesillas Yeshorim (Hebrew: מסילת ישרים, lit. "Path of the Upright") is an ethical (musar) text composed by the influential Rabbi Moshe Chaim Luzzatto (1707–1746). It is different from Luzzato's other writings, which are more philosophical.
Mesillat Yesharim was written and published in Amsterdam. The earliest known manuscript version, written in 1738, was arranged as a dialogue between a hakham (wise man) and a hasid (pious person). Before publication, it was rearranged to have only one speaker. The dialogue version often sheds light on the more well-known version.
Mesillat Yesharim is probably Luzzato's most influential work, widely learned in virtually every yeshiva since formal study of musar texts was introduced to the yeshiva curriculum by the Mussar Movement of Rabbi Yisrael Salanter.
The aim is the perfection of character. Unlike many other musar books, which are ordered according to the authors' own lists of character traits, Luzzato builds his work on a Beraita (quoted in many places, including (Bablylonian Talmud, Avodah Zarah 20b)) in the name of the sage Pinchas ben-Yair, whose list goes in order of accomplishment: "Rabbi Pinchas ben Yair said: Torah leads to watchfulness; Watchfulness leads to alacrity; Alacrity leads to cleanliness; Cleanliness leads to abstention; Abstention leads to purity; Purity leads to piety; Piety leads to humility; Humility leads to fear of sin; Fear of sin leads to holiness; Holiness leads to prophecy; Prophecy leads to the resurrection of the dead".
Within each step, Luzzatto explains the step itself, its elements, how it can be acquired, and what might detract from its acquisition. For example: Watchfulness can be acquired by setting aside time for introspection, and acquiring watchfulness can be impaired by excessive mundane responsibilities, wrong company or a cynical stance in life. The same pattern is used for every single one of the traits mentioned.