In Turkey, the demography studies of the history of the Ottoman classical period started with Omer Lutfi Barkan. He started writing in the early 1940s and focused in his work on the Ottoman institutions and the series of sources produced by these institutions. Further, he addressed the population issue based on these sources. Barkan was inspired by the works of the representatives of the Annales School that had been developing in France during the same period. Therefore, he compared especially the population data stated in Braudel's work known as Mediterranean World with the Ottoman resources, proving that the population growth seen all over the Mediterranean world in the 16th century was also the case for Ottoman geography. In this framework, he drew attention to sources such as the tahrir, avariz and cizye registers, which contain the appropriate data for the history of demography. Besides publishing some sections of these registers, Barkan compared these data with the findings of the Annales School. In fact, he put emphasis on how to use these records, which were primarily written for tax purposes, to find out about the history of population and underlined the possible problems related to this issue. One major problem, for instance, was the term hane. The hane was used as a tax unit in the registers, and according to Barkan, the coefficient had to be "5" to calculate the total population. However, according to estate-based studies made in the following periods, this coefficient should be revised as "4". A similar situation applies to the cizye registers. The hane and nefer terms used in these kinds of registers require the use of different coefficients. After the 1695 reform, the age for taxpayer registration in the cizye registers decreased. Therefore, the coefficient which had to be used to obtain the amount of population from these registers decreased to "2". In any case, all the data in the registers must be used carefully. On the other hand, problems like population density, growth rate, rural-urban distribution, and the calculation of the nomadic population are still being discussed among researchers today. According to recent studies, in some relatively settled areas like "Hudavendigar livasi", the average density of the population in the late 16th century was 20 persons per square kilometers. This is an average for regions like Bursa composed of crowded cities, but this average may decrease to a minimum of 7 in the mountainous regions. The horizontal and vertical mobility of the population are being examined in more social contexts. However, there is still a lot to be done to obtain integrated knowledge about the Ottoman population.