In the upsurge of research on bilingualism in the last two decades there have been some remarkable discoveries. Many of these findings have been replicated in subsequent studies, with little doubt remaining as to their veracity. To illustrate, we now assume that the bilingual’s two languages are continually active, creating a dynamic interplay across the two languages. What remains controversial about that? There continues to be controversy about the consequences of that cross-language exchange for how cognitive and neural resources are recruited during language use and whether native speakers of a language retain privilege in their first acquired language. Likewise, we now assume that in the earliest months of life, minds and brains are tuned differently when exposed to more than one language from birth. That tuning has been hypothesized to open the speech system to new learning. Why is that controversial? When initial exposure is to a home language that is not the majority language, the experience common to heritage speakers, the value of bilingualism has been challenged, in part because we are lacking an adequate account of the variation in language experience. The controversies that have arisen around research on bilingualism have had two sides. One is to provide an illuminating lens to the science and the other is to create a hotspot for opposing views. The best face of controversy is to reveal the limits of the past science, to push theory-driven discussion, to embrace serendipity, and to search with humility for the source of failures to replicate. By questioning the generality of accepted findings, recent studies have shown that the minds and brains of bilinguals are inherently complex and social, taking into account the variation in contexts in which the two languages are learned and used, and shaping the dynamics of cross-language exchange across the lifespan.