This report examines the academic literature on the role of families in the transmission of ideology. It sets out the results of a qualitative review, with particular reference to political and religious socialisation, and the transmission of extremist ideologies, but drawing on research from multiple disciplines, including political science, sociology, psychology, cognitive science, educational studies, religious studies and anthropology. This report is divided into three main sections, starting with an overview of some of the key theories that have informed the study of families and ideological transmission drawn from a wide variety of literatures. These include social learning theory, which underpins a great deal of research on the transmission of political values and practices (usually described as affiliations), habitus and embodied learning, cognitive transmission and other theoretical approaches to political and religious socialisation. The second section summarises empirical work relevant to the role of the family in ideological transmission. This ranges from detailed and extensive quantitative studies of political socialisation to in-depth ethnographic approaches that have attempted to document family influence on religious nurture. The final section focuses on examples of ideological transmission in families involved in political and religious extremism and terrorism. It sets out a number of case studies designed to illustrate specific points. Several of these cases focus on individuals who have been involved in terrorist activities, but the cases also include more typical examples of extremist ideological transmission.