Most programs to prevent and counter violent extremism (CVE) now include support programs for families of violent extremists. However, like many other CVE interventions and programs, the evidence base is still very limited. This article presents a literature review and a multi-method data assessment (including interviews with parents and family members of jihadist foreign fighters, with experts, focus groups with families of foreign fighters and policy makers) regarding the evidence base for family support programs in the CVE field. This fits within a recent trend to develop and apply evaluation to the CVE field. This article differs from other CVE evaluation studies, because it applies realist review and realistic evaluation ex ante rather than ex post. This article demonstrates that such an ex ante approach can contribute to the legitimacy, feasibility and effectiveness of CVE policy and prepare the ground for more thorough evaluation research.