PROJECT SUMMARY Attention deficit/hyperactivity disorder (ADHD) is often considered to be a disorder in children and adolescents, but is, in fact, diagnosed in 2.5% of adults as well. A main behavioral correlate of ADHD is the claimed increase in susceptibility to interference from irrelevant external sources. A prevailing view in the literature is that deficits in executive functions, especially control over interference, underlie ADHD symptoms (e.g., Barkley, 1997; Pennington & Ozonoff, 1996). Interference control is the ability to prevent interference due to resource or stimulus competition (Nigg, 2000). However, despite 20 years of research, empirical evidence for impaired interference control in ADHD patients remains inconclusive using model tasks such as the Simon task and the flanker task. This may be related to methodological issues that are present in such tasks that are typically used to assess interference control. The current application is based on a new approach to study interference control that can avoid these issues. The approach makes use of a “forced-response” method in which individuals’ responses in conflict tasks are required at a fixed time. This fixed time occurs at a variable time after the presentation of the imperative stimulus to which individuals must make a response, making it possible to capture responses at various points in the processing stream. The application includes experiments using this new approach, and it offers a computational framework to understand how interference control in ADHD individuals may be compromised compared to healthy individuals.