Mood and anxiety disorders are common during pregnancy and the postpartum period. The goal of this dissertation was to investigate factors specific to the perinatal period related to the development, treatment, and prevention of depression and anxiety. In Chapter 1, we investigated the role of a risk factor specific to the perinatal period: maternal attitudes. We developed a measure of this construct and used this measure to assess the relationship between these attitudes and symptoms of depression and anxiety among first-time pregnant and postpartum mothers. Dysfunctional maternal attitudes predicted symptoms of depression and anxiety, and these attitudes had incremental predictive validity over general cognitive biases and interpersonal risk factors. In Chapters 2 and 3, we conducted meta-analyses assessing the efficacy of interventions for depression among perinatal populations and investigated whether characteristics of study design and interventions were associated with systematic differences in effect sizes. In Chapter 2, we included 27 studies assessing the efficacy of treatments for depression during pregnancy and the first year postpartum. We found that interventions resulted in significant reductions in depressive symptoms from pre-treatment to post-treatment, and symptom levels at post-treatment were below cutoff levels indicative of clinically significant symptoms. At post-treatment, intervention groups demonstrated significantly greater reductions in depressive symptoms compared to control groups. In Chapter 3, we included 37 studies assessing the efficacy of preventive interventions for postpartum depression. We found that depressive symptoms at six months postpartum were significantly lower in intervention conditions as compared to control conditions, and there was a significant reduction in the prevalence of depressive episodes in treatment conditions compared to control conditions. These studies further our understanding of the processes that place women at risk for emotional distress in the context of pregnancy and the postpartum period and suggest that a wide range of interventions are effective for treating and preventing depression in this population.