Millions of people use addictive substances, such as alcohol and cocaine, however only a subset of individuals become dependent on these types of substances. Addiction can be thought of as a maladaptive decision-making process, driven by distinct neural regions. As behavior shifts from goal-directed to habit-based behavior, control of this behavior by corticostriatal circuits shifts from the associative circuit, which includes the dorsomedial striatum, to the sensorimotor circuit, which includes dorsolateral striatum. Once behavior becomes more habit-based, and control shifts to the sensorimotor corticostriatal circuit, actions become difficult to devalue. Thus, behavior becomes difficult to change. In this dissertation, I explore a behavioral shift to habit-based behavior as one potential way addiction can occur. I focus on the dorsomedial and the dorsolateral striatum and the role of these two regions in goal-directed and habit-based behavior, respectively, and the role of these two regions in drug-seeking behavior. In addition, I discuss the dorsomedial and dorsolateral striatum in relation to animal models of drug addiction that differentially seek drugs, and I discuss these two regions as potential biomarkers of addiction treatment. Finally, I relate previous research as well as my own research, presented throughout the dissertation, to human drug use and consider how analogues of dorsal striatum in the human brain might play a role in human addiction and addiction treatment. In all, consideration of addiction as a maladaptive decision-making process as well as understanding the neural correlates of this process may help to generate new ways of perceiving, studying, and treating addiction.