Ancient Iranians were Zoroastrians and as part of their religion they celebrated the last 10 days of the year in their annual obligation feast of all souls, Hamaspathmaedaya (Farvardigan or popularly Forodigan). They believed Farevashi (Foruhars), the guardian angles for humans and the spirits of the dead, would come back to Earth for a reunion. These spirits were entertained as honoured guests in their old homes, and were bid a formal ritual farewell at the dawn of the New Year. The ten-day festival also coincided with festivals celebrating the creation of fire and humans. During the Sasanian period, 7th century AD, this festival was divided into two distinct pentads, known as the lesser and the greater pentad or Panji as it is called today. Gradually the belief developed that the 'Lesser Panji' belonged to the souls of children and those who died without sin, whereas 'Greater Panji' was truly for all souls.

Spring housecleaning was carried out and bonfires were set up, on the rooftops, to welcome the return of the departed souls. Food was prepared and wine was poured just in the case the departed souls needed food and drinks. Small clay figurines in shape of humans and animals symbolizing all departed relatives and animals were also placed on the rooftops. Some Zoroastrians still follow this tradition with clay figurines if possible. Flames were burnt all night to ensure the returning spirits were protected from the forces of darkness. This was called the “Suri Festival”. There were gatherings in joyful assemblies, with feasts and communal consumption of food that was blessed ritually. Rich and poor met together and the occasion was a time of general goodwill when quarrels were resolved and friendships renewed. Even today many families visit graveyards and pray for their dead relatives just before No Ruz. This is considered a blessed act and is regarded as an obligation by many, especially if the dead person is a very close kin.

Modern Iranians carry out the spring-cleaning and set up bon fires for only one night on the last Tuesday of the year. Both the young and the old will leap over the fires with songs and gestures of merriment. In rural areas and remote villages flames are still burnt all night outside the homes, though people have no idea what this is all about. Until recently in parts of Azerbaijan all the Wednesdays in the month of Esphand, the last month of the year was devoted to one particular task related to New Years. For example, the first Wednesday was to clean or wash the carpets, while the second was to do No Ruz shopping. Sabzeh (green shoots) was grown on the third one while the last Wednesday was to fix items needing repair.

This festival was not celebrated on this night and in this manner before Islam and is a combination of different rituals to make them last. Islamic mythology is added on to it to make it last. Since, there was a lot of opposition (and still is) to pre-Islamic festivals by the Arab occupiers and the clergy in Iran. Islamic accounts trace the origin of burning fires on rooftops to a Muslim hero, Mukhtar, a supporter of the popular Shi’ite leader Ali and his family. He was very instrumental in popularizing Shi'ism in Iran. According to such accounts he revolted against the ruling Arab dynasty after his release from jail. He was going to attack and destroy all homes belonging to the enemy.

He ordered Shi’ite supporters to set bonfires on their rooftops so that they could tell the difference between the friends and the enemies. This happened on the night before the last Wednesday and since then Iranians celebrate the occasion. Such accounts clearly indicate the strategies Iranians adopted in order to save their ancient rituals. The festival is celebrated on Tuesday night to make sure all bad spirits are chased away and Wednesday will pass uneventfully. Some of the taboos are pre-Islamic. People do not travel on this day and sick people are not visited on this night. In Zoroastrian tradition illness was assumed to be associated with demons and these were avoided by staying away from the sick.

Today the occasion is accompanied by fireworks from locally made firecrackers. There is no religious significance attached to it any more and is a purely secular festival for all Iranians. On the eve before the last Wednesday, bonfires are lit through out the streets and back alleys, or inside walled gardens for the more wealthy. People leap over the flames while shouting “sorkhie tu az man, zardieh man az tu,” which means, “your fiery red colour is mine and my sickly yellow paleness is yours.” This is a purification rite and 'suri' itself means red and fiery.

The festivities start in the early evening. Children and fun-seeking adults wrap themselves in shrouds symbolically re-enacting the visits of the departed spirits. They run through the streets banging on pots and pans with spoons (gashog-zani or spoon banging) to beat out the last unlucky Wednesday of the year. They will knock on doors while covered and in disguise and ask for treats.

Wishes are made and in order to make them come true, it is customary to prepare special foods and distribute them on this night. Noodle soup called ash e Chahar Shanbeh Suri is prepared and is consumed communally. People passing by are served nuts and dried fruits. This treat is called ajeel e Chahar Shanbeh Suri and usually is a mixture of seven dried nuts and fruits, pistachios, roasted chickpeas, almond, hazelnuts, figs, apricots, and raisins. Local variations apply and the mixture is different according to the location and the group celebrating it.

People who have made wishes will stand at the corner of an intersection or hide behind walls to listen to conversation by people passing by. If there is anything positive and optimistic in the conversation, the belief is that the wish will come true or there is good fortune to be expected. This is called aal-gush meaning 'eavesdropping for one's fortune'. The night will end with more fireworks and feasts. Family and friends meet and with the more modern Iranians music and dance will follow.

In Iran, young Iranians have turned “Chahar Shanbeh Suri” into a major event aimed at ignoring many of the restrictions imposed on the youth. Until very recently, the festival was not officially acknowledged by the authorities. However, the mass celebration of youth partying jubilantly outdoors has forced the authorities to accept and regulate the event. The use of powerful firecrackers normally creates serious injuries and has compelled the government and security agents to try to impose more control.

Outside Iran the occasion is celebrated with thousands of participants in major cities. Large outdoor areas, such as parks, are leased or secured for the occasion with live music or DJs, dance, food, face painting, etc. for the children. Iranian restaurants will have special programs for the evening with pop music and special dishes. The large number of Iranians participating in the celebrations has made this occasion known in cities with large Iranian populations.