This chapter explores motor impulsivity, defined as the inability to withhold or delay a prepotent action, and its relevance to various clinical disorders. The discussion begins by outlining conditions where motor impulsivity is a defining feature, including the hyperactive/impulsive subtype of attention-deficit/hyperactivity disorder (ADHD) and several impulse-control disorders (e.g., oppositional defiant disorder or ODD). The abstract details common paradigms used for the reliable measurement of motor impulsivity, such as tasks assessing action restraint and action cancellation. This chapter then focuses on the neurobiological mechanisms underlying this form of impulsivity. It investigates the critical involvement of key brain circuits, including the cortico-basal ganglia-thalamo-cortical (CBGTC) loop, the salience network, and the mesocorticolimbic pathway. Furthermore, this chapter provides a comprehensive review of the complex interplay of several major neurotransmitter systems, specifically catecholamines, serotonin, glutamate, and the cannabinoid and opioid systems, in modulating the capacity for motor control and inhibition.