This paper identifies the mechanisms of early party identity socialisation within the family. Although the question of why individuals harbour a given set of political attitudes is central in political behaviour research, the process of early political socialisation has often been treated as a “black box” (Aggeborn and Nyman, 2021): our understanding of how parents transmit their attitudes to their children remains limited. Drawing on classic findings from the United States (e.g., Jennings et al., 2009), I propose a model of early political socialisation of party identity where parental partisanship, its stability, and strength determine the likelihood of parent-child party identity congruence. Moving beyond current literature, I argue that this process is driven by two mechanisms: parental political interest and parent-child contact. Political interest has previously been conceptualised as an ex-ante determinant of early political socialisation, but empirical evidence is mixed (Jennings et al., 2009; Dinas, 2014); I contend that it does not exert independent influence and is best understood as a moderator that either facilitates or hinders parent-child attitude transmission. Parent-child contact as a mechanism of early political socialisation is a relatively novel proposition: existing research accounting for the role of contact is limited to assessments of differential influences between mothers and fathers on their children (Zuckerman et al., 2007; Coffé and Voorpostel, 2010). I test the proposed model on data from the British Household Panel Survey and the UK Household Longitudinal Survey. The empirical strategy consists of a simultaneous equations model with a panel data estimator. Results TBC