There is increasing evidence for the intergenerational decline of religiosity across many different countries: religious beliefs, behaviours, and identities of parents are not being passed on to their children. This Element surveys the psychological and sociological research on the intergenerational transmission of religion, focussing on the factors that influence it. After introducing the topic in Section 1, Section 2 describes the methods used to study intergenerational transmission. Section 3 argues that the religious decline in recent decades is mainly due to intergenerational changes, as distinct from ageing or historical period effects. Section 4 examines societal and social factors, including national context, peers, education, religious communities, and the Internet. Section 5 focusses on parents, who are the most important agents of religious socialisation. Section 6 draws lessons from religious minorities, highly religious families, and also nonreligious families. Section 7 offers some practical conclusions for parents, and suggests directions for future research.