In recent years, promising steps have been made in identifying, sharing and implementing good practices in dealing with (returning) Foreign (Terrorist) Fighters (FTFs). This policy brief addresses capacity-building challenges in relation to the implementation of these good practices. It aims to do so by sharing some of the insights and progress made with regard to the capacity-building efforts developed by the International Centre for Counter-Terrorism-The Hague (ICCT) on the issue of FTFs in a selection of countries. The approach and outcomes of these capacity-building activities are linked to the recommendations in the Global Counterterrorism Forum's (GCTF) The Hague-Marrakech Memorandum on Good Practices for a More Effective Response to the FTF Phenomenon. Eight insights and recommendations are provided for policy makers and implementers alike, related to organisation, implementation, and monitoring of capacity-building efforts.