Yazidi society is divided into three hereditary and endogamous castes: the sheikhs and the pirs, both priestly, and the murids, the lay majority. Membership is by patrilineal descent and cannot be acquired. Marriage across the castes is forbidden, marriage to a non-Yazidi is forbidden, and there is no conversion in either direction: a person is born Yazidi or is not one. Every murid family is attached to a particular sheikh and a particular pir, and each individual also has a brother or sister of the hereafter, a spiritual sibling from a priestly lineage who attends them at death. Two offices stand above the structure: the Mir, the hereditary prince who is the community's temporal head, and the Baba Sheikh, its senior religious authority.
Transmission has been oral rather than textual. The content of the religion lives in qewls, hymns in Kurmanji Kurdish memorised and performed by a specialist class of reciters, the qewwals, together with prayers, stories, and the ritual practice itself, baptism in the White Spring at Lalish, pilgrimage, the seven-day autumn assembly, seasonal fasts and prayer turned toward the sun. Literacy was for centuries discouraged outside the priestly lineages, which reinforced the oral character and left the tradition without the kind of book outsiders expected to find.
Which is where the two texts usually named as Yazidi scripture come in, and they are a cautionary tale. Manuscripts of the Kitab al-Jilwa and the Mishefa Res circulated and were published in the early twentieth century and were taken by Western scholars as the community's hidden books. Scholarly opinion now generally holds those manuscripts to be forgeries, produced for a Western market by people who were not Yazidis. The judgement is qualified rather than simple: their contents draw on genuine Yazidi tradition and are not invented outright, and it remains open whether texts of those names existed in some other form. But older reference works were built on them, and accounts of Yazidism derived from that literature should be treated with care.