Purpose: This overview of reviews analyses the existing evidence base of functional family therapy (FFT), which is a manualized, family-based intervention for youth with behavioral problems and their families. FFT has been implemented among youth aged 10–18 at risk of, or presenting with, behavioral problems such as delinquency, violence, substance abuse, sexual perpetration, and truancy. Method: A multipronged search was conducted across 15 databases, 10 websites, and expert contacts in February 2018. Results: The search yielded 159 hits of which 31 were included and critically appraised. Included reviews were published between 1986 and 2018 and the number of included studies ranged from 1 to 18 (including 20–5,344 participants). Main effects of the intervention on core outcomes (recidivism and substance abuse) were modest and out-of-home placement was not reported. Secondary outcomes were also modest but generally positive. Conclusions: Findings demonstrate that overall quality of reviews is low, which makes any certainties about FFT inconclusive; this overview provides a concise, valid, and methodologically sound synthesis of the research into FFT, which requires more rigorous investigation.