Research on bilingualism has documented profound brain plasticity by which the bilingual experience reconfigures the cognitive system. These effects include temporary as well as more enduring ones, and parallel activation of a bilingual's two languages may well be a key factor at the root of these observed changes. Recent recommendations (Green, 2011) have emphasized that research on code-switching in particular could provide a fruitful avenue for investigating the nature of how a bilingual speaker selects words and ultimately produces an utterance. Findings to date illustrate that if anything, the reach of co-activation is more extensive than previously thought, extending to the phonology and syntax of languages. While the degree of permeability may compound the perceived difficulty of the selection process, it is also a testament to the documented mental agility of bilinguals.