As the most important female deity in the Iranian pantheon, Anāhitā has been the subject of a number of studies, but none as extensive or encompassing as what has been undertaken in this dissertation. Previous research on Anāhitā has tended to focus on specific aspects (such as linguistics or whether or not she is an "Iranian" deity), and has been largely limited to the periods of the three pre-Islamic Iranian empires. We, by contrast, have sought to incorporate the various questions addressed by previous scholars-alongside new ones of our own-within a cohesive narrative framework spanning four millennia up to the present age and drawing on a wide range of disciplines. In particular, reconstructing a proto-Indo-European water goddess through a comparison of Anāhitā with cognate figures from other cultures has not been hitherto attempted to the extent that has been done here, nor has the corpus of material on female literary and religious characters from the Islamic period previously been analyzed in terms of its possible connections to the Iranian goddess. In addition, we have advanced new arguments about the possible place of Anāhitā in Iranian and other Indo-European dragon-slaying myths. Anāhitā emerges in history by the late the Achaemenid period as one of the three principle deities of the Iranian pantheon, alongside Ahura Mazdā and Mithra; an important Avestan hymn, the Ābān Yašt, is composed in honour of Anāhitā, establishing her role within the Zoroastrian religion. During the course of this process she acquires additional functions, presumably from preexisting goddesses in the regions where Iranians came to live, from Central Asia (the Bactria- Margiana Archaeological Complex) to the Iranian plateau and Mesopotamia (Elamite, Sumerian, Bablyonian). Variations on the Iranian Anāhitā are found in the religious cultures of neighbouring lands such as Armenia, Bactria and Sogdiana. Her association with water enables us to connect her with the ancient Indo-European dragon-slaying myth as well as with the Zoroastrian saviour figure, the Avestan Saošiiant. The Sasanian royal family which ruled Iran from 224-651 CE was closely connected with the cult of Anāhitā, having been the hereditary custodians of her shrine at Eṣṭaxr during the preceding Parthian period; she remained the patron deity of the royal house throughout the Sasanian period. In the post-Sasanian Pahlavi texts her importance is much less than in the Avesta. Moreover, Anāhitā comes to be referred to as two distinct deities, Ardwī-sūr and Anāhīd, possessing both genders. This division and demotion is explained in light of priestly attitudes towards women and women's roles, particularly the construction of a "female" form of wisdom. We explain the ambivalence towards Anāhitā in the Pahlavi texts in terms of evidence of her connections to the planet Venus and to nocturnal daēva cults that were condemned by the Mazdaean priesthood. With the coming of Islam her cult disappears, yet numerous aspects of it survive in female figures from Persian literature and through folk tales and rituals, usually Islamicized, which are often connected with water. In one important example, it is proposed that Sūdābeh and Rūdābeh, two female figures in Ferdowsī's tenth-century Persian epic, the Šāh-nāmeh, are mythological reflections of two aspects of female power that can be connected with the ancient cult of Anāhitā. Further examples can be found in Iranian notions of female beauty and in superstitions about fairy figures (Av. Pairikās, NP Parīs), as well as in a number of popular rituals involving water which survive in Iran up to the present day. In sum, this dissertation schematizes the many progressive variations in terms of how Anāhitā was conceptualized and worshipped over time and space, in order to trace the goddess's development as a major figure in Iranian religion and the constantly evolving mix of her roles and attributes within culturally diverse communities throughout Greater Iran.