There are fears among Western governments about the growing threat posed by so-called ‘foreign fighters’ active in countries such as Syria and Iraq. It is now thought that over 3,000 Europeans have travelled to Syria, whether to fight or deliver humanitarian assistance. The profile of this cohort differs from the norm; there are a higher proportion of women, they are younger, and they are less likely to be known to the authorities. Both the nature and scale of the threat, therefore, are putting pressure on traditional intelligence and law enforcement-based approaches.