Yasna (; ) is the Avestan name of both a text within the Avesta collection and of the Yasna liturgy, Zoroastrianism's principal act of worship.
Overview
The function of the yasna ceremony is, very roughly described, to strengthen the orderly spiritual and material creations of Ahura Mazda against the assault of the destructive forces of Angra Mainyu. The yasna service, that is, the recitation of the Yasna texts, culminates in the apæ zaothra, the "offering to the waters." The ceremony may also be extended by recitation of the Visperad and Vendidad texts. A normal yasna ceremony, without extensions, takes about two hours when it is recited by an experienced priest.
The Yasna texts constitute 72 chapters altogether, composed at different times and by different authors.