This paper is intended to update the numbers of foreign fighters traveling to join the so-called Islamic State and other violent extremist groups in Iraq and Syria provided by The Soufan Group (TSG) in June 2014. Since then, other reports have emerged, including in September 2015 when United States intelligence estimates put the number of foreign fighters in Syria at upwards of 30,000 from over 100 countries. TSG research, which includes information provided directly by officials, largely
confirms these figures.

The numbers in this report have been compiled from official government estimates wherever possible, but also derive from United Nations reports, studies by research bodies, academic sources, and from other sources quoting government officials. Inevitably, whatever their source, the numbers quoted are subject to an inherent level of uncertainty. Many governments do not release official estimates of the number of their citizens who have gone to Syria and Iraq, and those that do, whether formally or informally, do not reveal their methodology and may struggle to achieve accuracy. Also, for some, the number may reflect all those who have gone, while others may subtract the number of returnees and/or those who have died. Some may not include women and children, while others do. It is rare that governments provide a detailed breakdown of their numbers and in all cases it is likely that more have gone than the relevant government is aware of or prepared to admit.