Theoretical models specify that anxiety aggregates in families. Research confirmed maternal anxiety as a predictor of childhood anxiety; however, very little evidence exists in support of paternal anxiety's role in child anxiety as well as about potentially reciprocal relationships between parental and child anxiety. The parent-child anxiety transmission mechanisms are also not fully understood; the majority of previous research focuses on the child's acquisition of anxiety symptoms from a parent via cognitive processes. Recent integrative theoretical models propose that child emotion regulation processes might be involved in parent-child anxiety transmission. The current dissertation aimed to address these gaps in literature. Both studies utilized data from over 800 mothers, 400 fathers, and their children drawn from the longitudinal NICHD Study of Early Childcare and Youth Development. Measures of maternal anxiety, paternal anxiety, child anxiety, and child emotion dysregulation were collected over a nine-year period when children were between the ages of 6 and 15 years. Study I provided evidence of significant indirect effects from parental anxiety to child anxiety through child emotion dysregulation for both mother-child and the father-child relationships. Child emotion dysregulation was non-significant in the father-child path of a family model, despite significant direct effects. The results provide evidence for child emotion dysregulation as an underlying process of parent-child anxiety transmission. Study II provided evidence of significant bidirectional predictive links of maternal anxiety and child anxiety across ages 6, 8, 10, and 15 years tested in a mother-child cross-lagged path model. Significant predictive paths from paternal anxiety to child anxiety were found from ages 6 to 8 and a significant predictive path from child anxiety to paternal anxiety was found from age 10 to age 15 in a father-child cross-lagged model. Additional tests of family models confirmed that there were unique effects of both maternal and paternal anxiety on child anxiety over time. The results show the long-term impact of both maternal anxiety and paternal anxiety on child anxiety as well as child anxiety's reciprocal effects on parental anxiety. Both studies demonstrate the importance of both mothers and fathers in childhood anxiety etiology.