The exact number of unwritten languages is hard to determine. Ethnologue (20th edition) has data to indicate that of the currently listed 7,099 living languages, 3,866 have a developed writing system. We don't always know, however, if the existing writing systems are widely used. That is, while an alphabet may exist there may not be very many people who are literate and actually using the alphabet. The remaining 3,233 are likely unwritten.