Modifiable health behaviors are a leading cause of mortality and chronic disease in the United States. Engagement in maladaptive health behaviors is linked to poor physical, psychological, and cognitive outcomes including increased risk of cardiovascular disease, Alzheimer's disease, anxiety, and depression. Using a neurobehavioral approach, I examined the hypothesis that neurobehaviors are impaired in clinical populations, and that exercise improves these neurobehaviors as well as the underlying mechanisms. In the first study, I found that a range of neurobehaviors are affected in individuals with obesity, indicating hyperactivity of the reward system and hypoactivity of the executive system. Using these neurobehaviors as predictors, I created a neurobehavioral model predicting obesity with an accuracy of 65%. In the second study, I examined neurobehaviors in a population of individuals in recovery from substance misuse. I found that neurobehaviors are altered in this population suggesting heightened activity of the executive system supports success in recovery. In the third study, I examined the effects of a long-term exercise program on a range of neurobehaviors and neurophysiology as measured through electroencephalography. I found that long-term exercise improved psychological state, memory, and attention. Additionally, I found that decreased cortical activity in response to exercise is associated with improvements in psychological state. Collectively, these findings suggest that there is a bi-directional relationship between the body and brain, with optimal physical health promoting optimal mental functioning. Additionally, these findings suggest that interventions that support improved neurobehaviors and neural circuitry are critical to promote engagement in positive health behaviors. / Doctor of Philosophy / Modifiable health behaviors are a leading cause of mortality and chronic disease in modern industrialized societies. Engagement in poor health behaviors is linked to increased risk of chronic disease affecting the body and brain including cardiovascular disease, Alzheimer's disease, anxiety, and depression. This dissertation explores the psychological and cognitive factors influencing engagement in healthy behaviors, and the ability of an exercise intervention to improve these factors as well as the underlying mechanisms. In the first study, I found that a range of neurobehavioral factors are impaired in individuals with obesity, and that these factors can be used to predict obesity. In the second study, I examined similar outcomes in a population of individuals in recovery from substance misuse, and found that neurobehaviors are altered in this population suggesting heightened activity of the executive system which supports successful recovery. In the third study I found that long-term exercise improved psychological and cognitive outcomes. Additionally, I found that changes in the electrical activity of the brain in response to exercise are associated with improvements in psychological state. Collectively, these findings suggest that there is a bi-directional relationship between the body and brain, with optimal physical health promoting optimal mental functioning. Additionally, these findings suggest that interventions that support improved neurobehaviors and neural circuitry are critical to promote engagement in positive health behaviors.