The purpose of this Notice of Funding Opportunity (NOFO) is to encourage clinical research that will identify and validate novel targets for non-invasive brain stimulation (NIBS) and SUD-relevant neurobiological, cognitive, and behavioral responses to NIBS that precede clinical outcomes like reduced craving or drug use. Applications are expected to be exploratory and developmental in nature. As such, these studies may involve considerable risk of failure but may lead to a breakthrough in a particular area that could have a major impact on SUD research involving NIBS. This NOFO uses a R61/R33 Phased Innovation award activity code to support applications that propose mechanistic studies designed to understand a behavior or biological process, the pathophysiology of a disease, or the mechanism of action of an intervention. In addition, applications must meet the NIH definition of a clinical trial. NIH defines a clinical trial as A research study in which one or more human subjects are prospectively assigned to one or more interventions (which may include placebo or other control) to evaluate the effects of those interventions on health-related biomedical or behavioral outcomes. (NOT-OD-15-015)