Rosh HaShanah is the only festival observed for two days both in Israel and the Diaspora (outside Israel).
Hallel (joyful psalms of praise to God) are not said on Rosh HaShanah – it is felt inappropriate to say Hallel during the Days of Awe when we are very conscious that God is sitting in judgment over us.
We read our prayers at this time from a special prayer book called a Machzor. "The Kingship of God" is the dominant theme of the Rosh HaShanah Machzor. It includes selections chosen from the Bible, Talmud, Midrash and medieval Jewish literature, and is as relevant today as when first written.
