This chapter discusses the challenges and benefits of including fathers in intervention programmes during the perinatal period, as well as exploring the impact of paternal mental illness at this time. The NSPCC's 'Dad Project', published as part of the All Babies Count campaign, indicated that many fathers feel isolated during the perinatal period because attention is focused on the mother and baby, and that many dads do not therefore get the support they need. This is surprising as we know that men also suffer from mental health difficulties during the perinatal period. The chapter focuses on paternal perinatal depression as this is the most widely studied mental health difficulty, although there is a growing evidence base for the impacts of other disorders. A review by Panter-Brick and colleagues highlighted the issue of father engagement in parenting interventions. It identified important potential barriers to consider in the design, implementation and evaluation of co-parenting interventions in order to engage men.