According to various studies and reports, Tunisia has been one of the top exporters of foreign terrorist fighters. This paper seeks to analyse the causes and factors underpinning flows of Tunisian foreign fighters. It will be argued that in Tunisia's case, the role of domestic mobilization structures played a key role in determining the amplitude of the foreign fighter phenomenon. In particular, Ansar al-Shari'a in Tunisia's (AST) efforts to structure the Jihadi-Salafi community into a large grassroots movement were instrumental in creating a wide pool of potential foreign fighters. Whilst the existence of a domestic grassroots movement made outflows of foreign fighters possible, these flows were motivated and oriented by the evolving geographical distribution of political and military opportunities across the Middle East and North Africa region. Indeed, new threats to the survival of the Tunisian jihadi movement manifested by the government crackdown on AST in 2013, in conjunction with the expansion and consolidation of the Islamic State in Iraq and the Levant, generated a significant outflow of Tunisian foreign fighters to Syria and Iraq. From the Islamic State's core territory, de-territorialized Tunisian fighters saw an opportunity to reconnect with their homeland in engaging in competition with al-Qaeda for the control of AST's legacy networks in Tunisia. During this whole period, neighbouring Libya played an important role as a line of flight or a foreign fighter corridor between Tunisia and Islamic State's core territory, until the centre of gravity of the Tunisian jihadi system shifted towards conflict-affected Libya when it became the host of three Islamic State provinces.