The finding that values, attitudes, and behaviour can be transmitted across generations is long standing. However, the role of fathers in this process has been underinvestigated. Furthermore, many researchers have not tested moderation effects. We extended the literature by investigating maternal and paternal transmission of harsh parenting beliefs to their children 23 years later. Furthermore, we examined the moderating role of interaction quality and included gender and socioeconomic status as control variables. Our data were collected in a unique longitudinal study of 128 families across 23 years. We found high positive associations between the harsh parenting beliefs of parents and their adult children, but only the mother–child transmissions were moderated by interaction quality. Mothers pass on low levels as well as high levels of harsh parenting beliefs to their children if their interaction quality is poor. These findings highlight the importance of investigating intergenerational transmission in both mother–child and father–child dyads.