The chapter describes al-Qaida’s contributions on the Taliban’s frontlines, mainly north of Kabul, in 1997-2001. It argues that al-Qaida participated with some of its best cadre on the Taliban’s frontlines to help the Taliban consolidate its power in Afghanistan. In 2001, al-Qaida became part of the Taliban’s foreign contingent called Brigade 19, which was numerically dominated by Uzbeks and Pakistanis. In general, al-Qaida was militarily insignificant but was able to contribute in key areas such as mine clearing and assassination operations, including the assassination of the Northern Alliance leader Ahmed Shah Massoud on 9 September 2001. Over time, al-Qaida’s frontline participation with the Taliban became an integrated part of al-Qaida’s own training and education programme. The existence of active frontlines in Afghanistan served al-Qaida’s own interests. The frontlines attracted recruits and they served as testing and training grounds for future al-Qaida cadre. Al-Qaida’s international terrorist operation could not possibly attract, absorb and test prospective members of al-Qaida the same way as the frontlines did. In other words, al-Qaida was dependent on having access to a frontline in order to build a resilient organization.