Fear is an adaptive emotion that typically increases across infancy to help keep infant exploration in check. Too much fear, however, can become maladaptive and lead to psychopathology later in childhood. Thus, it is important to understand how both fear reactivity and regulation develop early in life in order to identify at-risk children early on. Maternal factors, such as parenting behaviors and personality, are associated with both fear reactivity and regulation, but results have been mixed, possibly due to a trait-based approach to assessing maternal personality. The goal of my dissertation was to examine the growth trajectories of fear reactivity and regulation across infancy and toddlerhood both unconditionally and within the contexts of maternal parenting and personality functioning. Infants and mothers were assessed when infants were 10-months (n = 48), 14-months (n = 42), and 18-months (n = 34) old. At each age, infant fear reactivity was assessed using behavioral coding during the Laboratory Temperament Assessment Battery fear tasks and infant fear regulation was examined via respiratory sinus arrhythmia reactivity during the fear tasks. At 10- and 14-months, maternal parenting behaviors were coded during an interaction task and maternal personality functioning was assessed via maternal self-report. Hierarchical linear modeling demonstrated that maternal personality functioning moderated the association between maternal affect and infant fear reactivity growth and maternal personality functioning moderated the association between maternal directiveness and infant fear regulation growth. These results aid in the understanding of how maternal factors relate to infant fear development. / Doctor of Philosophy / Fear is an adaptive emotion that increases across infancy to help keep infants safe as they gain the ability to explore their environments independently. Some infants, however, exhibit heightened levels of fear that set them on a path for negative consequences, like anxiety disorders, in childhood. This typically occurs when infants have high levels of fear without appropriate regulation strategies to manage such. Maternal factors, like parenting behaviors and personality, have both been shown to affect the development of fear and the regulation of fear, but results are not consistent. Given this, the goal of my dissertation was to examine how level of fear (fear reactivity) and management of fear (fear regulation) develop across infancy and toddlerhood under the context of maternal parenting and personality. Infants and mothers were assessed when infants were 10-months (n = 48), 14-months (n = 42), and 18-months (n = 34) old. At each age, infant fear reactivity was assessed using behavioral coding during the Laboratory Temperament Assessment Battery fear tasks and infant fear regulation was examined via physiological means based on heart rate. At 10- and 14-months, maternal parenting behaviors were coded during an interaction task and maternal personality functioning was assessed via maternal self-report. Results demonstrated that maternal personality functioning moderated the association between maternal affect and infant fear reactivity development and maternal personality functioning moderated the association between maternal directiveness and infant fear regulation development. These results aid in the understanding of how maternal factors relate to infant fear development.