Transcranial direct current stimulation (tDCS) induces stimulation polarity-dependent neuroplastic excitability shifts in the human brain. Because it accomplishes long-lasting effects and its application is simple, it is used increasingly. However, one drawback is its low focality, caused by (a) the large stimulation electrode and (b) the functionally effective reference electrode, which is also situated on the scalp. We aimed to increase focality of tDCS. This might improve the interpretation of the functional effects of stimulation, because it will restrict its effects to more clearly defined cortical areas. Moreover, it will avoid unwanted reversed effects of tDCS under the reference electrode, which is of special importance in clinical settings, when a homogenous shift of cortical excitability is needed. Since current density (current strength/ electrode size) determines the efficacy of tDCS, increased focality should be accomplished by (a) reducing stimulation electrode size, but keeping current density constant or (b) increasing reference electrode size under constant current strength. We tested these hypotheses for motor cortex tDCS. The results show that reducing the size of the motor cortex DC-stimulation electrode focalised the respective tDCS-induced excitability changes. Increasing the size of the frontopolar reference electrode rendered stimulation over this cortex functionally inefficient, but did not compromise the tDCS-generated motor cortical excitability shifts. Thus tDCS-generated modulations of cortical excitability can be focussed by reducing the size of the stimulation electrode and by increasing the size of the reference electrode. For future applications of tDCS, such paradigms may help to achieve more selective tDCS effects.