Attention Deficit Hyperactivity Disorder (ADHD) is a prevalent neurodevelopmental condition marked by inattentiveness, hyperactive behaviors, and impulsivity. While pharmacological treatments provide clinical benefits for some patients, many individuals experience suboptimal therapeutic outcomes or adverse side effects. Emerging non-pharmacological approaches—particularly transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS)—demonstrate promising potential for alleviating ADHD symptoms through targeted neuromodulation. These techniques may offer viable alternatives for medication-resistant patients or those seeking to minimize pharmaceutical interventions. Nevertheless, considerable variability persists across studies due to divergent treatment protocols (e.g., stimulation parameters, target brain regions), participant demographics, and intervention durations. This chapter systematically examines these critical sources of heterogeneity.