Little is known in cognitive neuroscience about the brain mechanisms and brain representations involved in bilingual language processing. On the basis of previous studies on switching and bilingualism, it has been proposed that executive functions are engaged in the control and regulation of the languages in use. Here, we review the existing evidence regarding the implication of executive functions in bilingual processing using event-related brain potentials and functional magnetic resonance imaging. Several brain potential experiments have shown an increased negativity at frontocentral areas in bilinguals, probably related to the activation of medial prefrontal regions, for different tasks, languages, and populations. Enhanced cognitive control is required in bilinguals, which also involves the recruitment of the left dorso-lateral prefrontal cortex. The degree of activation of this mechanism is also discussed considering the similarity of languages in use at the lexical, grammatical, and phonological levels. We propose that the prefrontal cortex probably mediates cognitive control in bilingual speakers through the interplay between a top-down selection-suppression mechanism and a local inhibitory mechanism in charge of changing the degree of selection-suppression of the different lexicons.