The first chronologically comprehensive and conceptually sound view of conversion to Islam was that offered by R. W. Bulliet. His Conversion to Islam in the Medieval Period, published in 1979, is of great importance to the study of the conversion process and its ethno-religious and social consequences. Qualifying R. W. Bulliet’s method as “an original, bold and provocative work worthy of attention,” it should be mentioned that his study has been criticized on many grounds. Some historians conceive it, above all, as “food for thought,” its conclusions being reliable primarily with respect to medieval Iran only, due to the great limitations of the source base. I would maintain, however, that given the sufficient amounts of available empirical data, R. W. Bulliet’s research technique is reliable and meaningful. In my paper I have attempted to show through the results of my research that his quantitative model and timetable of conversion to Islam are valid in relation to the investigation of the dynamics of ethno-religious processes in the Ottoman Balkans. The similar results revealed in both this researcher’s theoretically drawn model and the curve of conversion that I obtained when using a sufficient quantity of numerical data from the Balkans, prove that Bulliet’s method is applicable in investigating the diffusion of Islam in its broadest chronological and territorial scope.