Dopamine is a major neuromodulatory agent of the central nervous system. The neurotransmitter has a non-linear dose-dependent effect on cortical excitability and activity, which depends on spontaneous activity, dopamine concentration, and dopaminergic sub-receptors, amongst others. By its impact on cortical and subcortical network activity and excitability, dopamine modulates such cognitive performance as attention, as well as learning and memory formation. Although animal studies have enhanced our knowledge about the physiology of dopamine considerably, the transferability of the results to conscious humans is limited due to altered spontaneous neuronal activity in anesthetized animals or slice experiments. Recently emerged noninvasive brain stimulation techniques enable the exploration of cortical excitability in humans. Here we review the respective experimental results and derive conclusions about how dopamine might affect the cortical excitability of the human brain.