Among the most widely read books in the Ottoman world were ilmihals, manuals of religious instruction that were written to teach ordinary believers the basics of Islamic doctrine and practice. The genre’s origins lie in the aqa’id works, Islamic creeds, the later examples of which also incorporated matters of religious practice alongside doctrine. The earliest known Turkish ilmihals, dating from the fourteenth and fifteenth centuries, were, in large part, translations-cum-adaptations of such creedal works, but they also covered various topics that would normally come under the purview of conduct books and books of practical ethics. As such, ilmihals fulfilled both a more local need to transplant knowledge of Islamic norms to the lands of Rum and a more general tendency in the post-Mongol period to codify Islamic belief and practice. This second dimension of ilmihal writing became even more important when the Ottoman state elites embarked upon a project of Sunnitization in the sixteenth century. It was also in this period, and particularly after the late sixteenth century, that the genre truly proliferated. Many more ilmihals were written then, and circulated in greater numbers, a development that was aided by the spread of literacy among the urban populace. Moreover, even though ilmihals were written with the explicit aim to homogenize Islamic belief and practice, the genre itself became diversified in the first half of the seventeenth century, when the top ranks of the learned establishment lost their monopoly over the religious debates, and when a socially and ideologically more diverse group of writers turned ilmihals into a platform for religious controversy. The present paper also focuses on this rather prolific period of ilmihal writing, running from ca. 1550 to ca. 1660. The 110 years in question are examined both as a distinctive “moment” in the longer history of the genre, and as a period in which the genre went through different phases in line with the rapidly changing social, political and religious climate. A central concern of this investigation will be to map out the principal textual communities that produced and circulated ilmihals. To this end we shall examine which texts tended to go with which, and the intellectual genealogies claimed for each text. We shall also examine how the content and form of ilmihals varied according to the social profile of both the writers and the intended audience.