The purpose of this book is the survey of the processes that are related to phonological rules and conversion of each of them, in varieties of Iranian languages on the basis framework of Generative Phonology. For this purpose, 70 varieties of Iranian languages have been selected purposefully then the historical form of data have been extracted by the using of the historical resources and finally for discovering the natural rule, authors have analyzed these rules according to criteria that Jensen (2004: 117) has proposed in phonological analysis of rules.