The Passover Seder is a ritual feast at the beginning of the Jewish holiday of Passover. It is conducted throughout the world on the eve of the 15th day of Nisan in the Hebrew calendar. The day falls in late March or in April of the Gregorian calendar. Passover lasts for seven days in Israel and, among most customs, eight days in the Jewish diaspora. Where seven days of Passover are observed, a seder is held on the first night; where eight days are observed, seders are often held on the first two nights, the 15th and 16th of Nisan. The Seder is a ritual involving a retelling of the story of the liberation of the Israelites from slavery in ancient Egypt, taken from the Book of Exodus in the Torah. The Seder itself is based on the Biblical verse commanding Jews to retell the story of the Exodus from Egypt: "You shall tell your child on that day, saying, 'It is because of what the LORD did for me when I came out of Egypt.'" At the seder, Jews read the text of the Haggadah, an ancient Tannaitic work. The Haggadah contains the narrative of the Israelite exodus from Egypt, special blessings and rituals, Talmudic commentaries, and Passover songs.