Elements such as water and fire were personified. Water itself became a goddess, the 'Apas' (modern Persian ab), with specific prayers and libations made to her. The elders of each household made regular offerings (either plants or animals) to the nearest pool or spring, where there were communal ceremonies involving the priestly rites. Fire, named atar (modern Persian azar / atash) was also worshipped with offerings consisting of clean dry fuel, incense and animal fat, if available.

The offerings to the elements of fire and water formed the basis of the daily priestly act of worship called by the Iranians 'yasna' (from the verbal root yaz- sacrifice, worship). Animal sacrifices were made to the fire cult and prayers consecrated the act. They believed that there was strong kinship between humans and animals, and the spirits of animals, which died a sacred death, became absorbed in a divine being called Geush Urvan, the 'Soul of the Bull'. Urvan is ravan in modern Persian meaning soul and Geush Urvan became another important cult and protector of all useful animals on earth. Another major cult grew out of the ritual of preparing a sacred juice from a plant called 'soma' by Indians and 'haoma' by the Iranians meaning 'that which is pressed'. It was very likely produced from a species of ephedra and was assumed to have great qualities. It inspired warriors, poets and storytellers, and also caused priests to become more open to divine prompting after ceremonial drinking. The cult of the sacred juice is still practiced today by Zoroastrians.

Proto-Indo-Iranians worshiped many gods including several 'nature gods', such as Asman, the Lord of sky (aseman ; sky in modern Persian), Zam, the earth goddess (zamin in modern Persian) and the sun and the moon, Hvar and Mah (khorshid and Mah in modern Persian). In addition, there were the two gods of the Wind, Vata and Vayu, the wind that blows and the wind that brought the rain clouds. Vata the rain-bringer was associated with 'Harahvati Aredvi Sura', the Sanskrit Sarasvati meaning 'Possessing waters'.

She personified a mythical river, believed to pour down from a great sea called in Avesta, Vourukasha, meaning 'of many bays', a sea out of which all rivers flow. Tishtrya, meaning 'the God of the Dog Star' protected the clouds that brought rain. Every year he goes to the shores of Vourukasha in the shape of a splendid white stallion and fights the Demon of Dearth, Apaosha, in the form of a black stallion. Then Tishtrya rushes into the sea and the waves through encounter with Tishtrya produced water in abundance. Vata snatches the waters up into the clouds and scatters it all over the) 'haft kashvar' (seven countries). Zoroastrians had a major celebration for Tishtrya around 13th of Farvardin (the first month of the Iranian calendar), the time Iranians celebrate as Seezdeh be-dar, and till 19th century there were horse races on this day. This was very likely the continuation of the tradition of ancient festivals re-enacting the myth of the battle of the stallions. Iranians still make offerings to water on the 13th of Farvardin by throwing their 'sabzeh' (green shoots used at No Ruz, a plant offering) into the waters.

The Indo-Iranians believed there was a natural law which ensured that nature followed its course. Day and night continued and sun maintained its regular movement. They called this law 'rta' ( 'asha' in Avesta) that came to represent the cosmic order. Asha had ethical implications and governed human conduct as well. Truth, honesty, loyalty and courage were praised with virtue as necessary for the natural order and vice was identified (you needed a verb here) as disturbing to this order. The principle of falsehood or distortion, which was opposed to asha in Avestan literature, is called 'drug' (lie, false). One vital aspect of asha was to enforce respect for the sacredness of a man's given word. The solemn oath was called 'Varuna' (ver means tie, bound) and the covenant was called 'Mithra' (from the root mei meaning exchange). In both cases a power felt to be latent in the spoken pledge came to be recognized as a divinity. Men accused of breaking their words were punished by being submitted to an ordeal by water (immersed under water, if survived declared innocent) or fire. The accused would have to run along a narrow gap between two blazing piles of fire (as in the story of Siavash in Shahnameh) or molten copper was poured on their bared breast.

Mithra and Varuna became divinities linked with fire and water. Varuna became 'Son of the Waters', and later evolved into Varuna Apam Napat, the yazata (eyzad) of the oath and truth and lord of the ordeal by water. Mithra eventually evolved into the lord of fire and covenant and was believed to accompany the sun itself. The decision to allow men to be subjected to such dangerous ordeals was made by the local ruler or the elder of the community. This figure of the wise ruler, in ultimate control of the law, seems to have been the origin of the concept of 'Ahura Mazda', the lord of wisdom, the greatest of all the lords. The three lords are highly ethical beings, who uphold asha and this concept evolved amongst the proto-Indo-Iranians early in the Stone Age.

There also existed a number of abstract gods personifying concepts such as war. For example, Mithra was also worshipped as the war-god, fighting on behalf of the good and protecting the virtuous. Latter on, he is personified as both a great judge assessing the deeds of men after their death and as a solar deity to be drawn across the sky by white horses, shod with silver and gold, without casting a shadow. This latter characteristic has survived in Islamic literature wherein great religious men have no shadow. Airyaman was the divinity personifying friendship; Arshtat represented Justice; Ham-vareti, courage; and Sraosha (Soroush) was obedience. 'Verethraghna', god of victory, became a prominent deity in the later Avestan literature.

Most of the Indo-Iranian gods were anthropomorphic (human-like), however Verethraghna resembles a wild boar and all these gods were assumed to be immortal. A cosmology evolved and the first creation myth of the Iranians belongs to this period. "The gods created the world in seven stages. First they made the sky of stone, solid like a huge round shell. In the bottom half of this shell they put water. Next they created earth, resting on water like a great flat dish; and then at the center of the earth they fashioned the three animate creations in the form of a single plant, a single animal (The bull) and a single man (Gayo-maretan, 'Mortal Life', Kewmarth in modern Persian). Seventh, they created fire, both visibly and as a vital force. The sun, part of the creation of fire, stood still overhead as if it were always noon. The world was motionless and unchanging, and then the gods offered a triple sacrifice. They crushed the plant, and then slew the bull and the man. From this sacrifice came more plants, animals and humans. The cycle of life was set in motion and death was followed by new life. The sun began to move across the sky to regulate the seasons in accordance with asha (in Zoroastrian literature this day is called the first No Ruz).

The Indian sources indicate that these natural processes were regarded as never-ending as long as men and the priests did their part. By praying, making sacrifices and libations humans became partners with gods in maintaining the world in a state of strength and purity. Rituals and ablutions, particularly prayers, were required and patterns emerged that would stay with Iranians for centuries to come. Pagan Iranians prayed three times per day (sunrise, noon and sunset), and the daylight hours were divided into two periods. The morning one was under the protection of Mithra while Apam Napat protected the afternoon. Fravashis (fereshteh in modern Persian), the spirits of the dead, protected the nighttime. Several of these concepts remained and were adopted by the Zoroastrians. Many are still present in Zoroastrian (and even Islamic) literature though changes were introduced and the new cosmology introduced by Zoroaster differed from the ancient one in a number of ways.