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 Yisroel Salanter. Source: Wikipedia (en)