Yom Tov Shel Rosh Hashana: 5666 (Hebrew: ספר המאמרים תרס״ו), known in Chasidic reference as Samech Vov, is a compilation of the Chasidic treatises by Rabbi Sholom Dovber Schneersohn, the fifth Rebbe of Chabad, from the Hebrew year 5666 (1905–06).

This series of Chassidic essays is considered a fundamental work of Chabad mysticism.

[2] The work is titled as Yom Tov Shel Rosh Hashana after the opening words of the first treatise.

The central theme in the series is the concept of Dira Betachtonim, the process of "making the world a dwelling place for God".

[2] The concept of a divine dwelling is attributed to a statement in Midrash Tanchuma, an Talmudic book of homilies, “God had a desire to have a home in the lower world.”[3][4] Samech Vov is styled as a series of discourses.