Invisible Walls Wales (IWW) is a Big Lottery funded project based in HMP Parc, South Wales, aimed at maintaining and improving relationships between male prisoners and their children and families, improving the quality of life of all participants, reducing re-offending by the prisoners, and reducing the risk of ‘intergenerational’ offending. It adopts a ‘whole family’ approach, providing support to prisoners, partners and children for up to 12 months pre-release and six months post-release via three integrated ‘hubs’ of activity (prison, transitional and community). Key elements of the project are the Family Interventions Unit (FIU – the first of its kind in a male prison in the UK), interventions-led visits in family-friendly facilities, through-the-gate casework by Family Integration Mentors (FIMs), and partnership with community-based agencies. While the initial funding for the project ended in 2017, IWW has evolved into an ongoing (albeit reduced) service with joint funding from G4S and Her Majesty’s Prison and Probation Service. This report presents the results of an evaluation conducted between 2012 and 2017, to assess IWW in terms of the quality and effectiveness of its organisational processes and practices, and its impact on all participants (including children).