Over the past two decades, there has been an explosion of tools that allow researchers to manipulate and observe the function of specific neural populations and their projections. These tools, including optogenetics, chemogenetics, cell-type-specific ablation, and fluorescent calcium indicators, have been especially useful in studying the function of cell types in the basal ganglia, where the majority of neurons are essentially indistinguishable by morphology or physiology. Although recent work has mostly supported the classical model of basal ganglia structure and function, cell-type-specific methods have revealed nuances in the role of striatal circuits in reward and action selection. These tools have also provided evidence for an expanded role of the basal ganglia in reinforcement and emotional states. Moving forward, new technologies will be needed to study the basal ganglia on a circuit level to better understand how cell types interact to shape behavior.