Zoroastrianism, in spite of its small current number of adherents, has played a huge role in the study of comparative religion. Not only was it a cohort of the ancient Vedic Hinduism, but also had a huge influence on the development of Judaism and Christianity.
The Sacred Text of Zoroastrianism is the Avesta, some times called the Zend Avesta. The Persian Avesta and the Indian Rig Veda are considered foundation documents in the study of the Indo-European languages. There are also many correspondences in religious belief, gods (Mithra & Mitra), and culture between these two ancient Texts, which share a common genetic origin. There are also large differences in belief with many gods (Devas) of the Rig Veda, becoming Demons in the Avesta. Variations of the Soma/Haoma ceremony are found in both of these Texts, leading to the conclusion that the ancestral Soma ceremony obviously predates either Texts creation.
Sacred-texts Zend Avesta 1
Sacred-texts Zend Avesta 2
Sacred-texts Zend Avesta 3