Childhood emotional maltreatment is associated with damaging consequences, although relatively little is known about the mechanisms underlying its effects. This dissertation investigated the concurrent influences of adult attachment and mindfulness on internalizing symptoms and emotional processing in young adults with and without a history of emotional maltreatment. Study 1 revealed that a sequential mediation model, with adult attachment orientations as first-step mediators and mindfulness as a second-step mediator, fit the data better than a simultaneous mediation model. In addition, moderation analyses revealed that high self-reported levels of mindfulness protected against the development of internalizing symptoms, even in at-risk individuals. Study 2 replicated these findings in a new sample, while also extending the results beyond a self-report outcome, using behavioural measures of emotional processing. Emotional maltreatment, adult attachment, and mindfulness predicted the amount of perceptual information required to correctly identify fearful faces and the amount of interference demonstrated in response to positive and negative emotional words. Cumulatively, these findings suggest that childhood emotional maltreatment can disrupt attachment relationships and encumber the development of mindfulness, contributing to internalizing symptoms and the biased processing of emotional information. However, alternative outcomes are possible, given the presence of high levels of mindfulness and secure attachment representations. This has implications for clarifying developmental theories and evaluating clinical interventions that may mitigate the negative effects of childhood emotional maltreatment.