Now Ruz is a national holiday which celebrates the Persian New Year. Now Ruz is celebrated by many groups in Iran. The date of Now Ruz is determined by a solar calendar (unlike the rest of the Muslim world which uses a lunar calendar) and begins on the first day of spring, when the sun enters the zodiacal sign of Ram. The festival of Now Ruz lasts for thirteen days and is a time of renewal and great joy.

The origin of Now Ruz is traditionally attributed to the legendary King Jamshid, the most powerful of the kings of Persia. This legend is recorded by Tabari, Biruni, and Ferdowsi. One version says that Jamshid taught his people the arts of building, weaving, mining and making weapons, and divided them into four classes. Jamshid set out to conquer the demons. He defeated the demons and ordered them to build a crystal carriage. When it was finished, Jamshid entered the carriage and the demons lifted it into the air and took him from Demavand to Babylon. The day was called Now Ruz (the New Day) and was made an annual celebration.

A more realistic explanation is that the Now Ruz festival is an agrarian celebration. It owes its origin, to some degree, to the fertility cult, which was common in the ancient Near and Middle Eastern. Some of the customs observed at Now Ruz are similar to the Babylonian Zagmuk. The growing of sabzeh (or fresh greens), which are later thrown into the water, is similar to the practices of the Syrian cult of Adonis. Ancient and Zoroastrian Persian culture are the sources of the customs and ceremonies of Now Ruz.

Muslims use the lunar calendar to determine the timing of holidays. Now Ruz is determined by a solar calendar. This solar calendar was adopted by the ancient Zoroastrians, and is the national calendar of Persia. According to Persian legend, the earth's axis spins on one horn of a giant bull. Once a year, during the vernal equinox, the bull tosses the earth from one horn to the other. His movements are so smooth that this shift can only be detected by observing the movements of an egg on a polished surface. Members of the family gather to watch the egg and, if the egg does not move at the proper time, an adult taps it.