This paper on conversion to Islam rely on the şer'iyye sicils of Kayseri. It beings by reviewing the traditional Turkish concept of State in conjuntion with the archival evidences. By examining the court cases in these sicils it will be possible for us to assess how the non-Muslim conversion to Islam took place in the Ottoman society as seen from this sicils of Kayseri for the period 1645-1665. The result of this examinations will help to revise a member of misconceptions regarding conversion in the Ottoman Empire a study of conversion from the sicils may yield a certain insight into the nature of the relationship between tne centre and people