Addressing a gap in process-oriented understanding of relations between marital conflict and children's adjustment, propositions of the emotional security hypothesis from a family-wide perspective were tested in a longitudinal research design. Participants were 181 families and their 11-12 year-old-child (115 boys, 76 girls) living in Wales, in the United Kingdom. Relations between marital conflict, children's emotional security about marital conflict and parenting, respectively, and children's adjustment were assessed based on reports by mothers, fathers, and children and videotaped analogue procedures completed by children. Structural equation modelling indicated that children's emotional security about interparental conflict (emotional regulation, cognitive representations and behavioural regulation) mediated the relation between marital conflict and children's security about parenting. Processes pertaining to children's security in multiple family systems (i.e., interparental and parent-child) provided an indirect mechanism through which interparental conflict affected children's symptoms of psychological distress (internalising and externalising problems) assessed 12 months later. Future directions for further tests of comprehensive, theoretically based models for the effects of marital conflict on children are discussed.