The author has spent a large part of his research career studying spoken language processing in bilinguals. In this chapter, he first gives a brief overview of the stages involved in speech perception and comprehension; that is, how the listener goes from the acoustic wave all the way to the interpretative representation. He then describes a number of studies he undertook that concern primarily the processing of bilingual mixed speech. The research deals with the gender marking effect (late bilinguals appear to be largely insensitive to gender congruency and incongruency), the base-language effect (in normal bilingual discourse, base‐language units – i.e. phonemes, syllables and words – are favored over guest‐language units, at least for a short period of time), and the recognition of guest words. Here, the author showed evidence for a number of effects that occur when guest words are recognized in bilingual speech, such as a language phonetic effect, a phonotactic effect, an interlanguage homophonic status effect, and a base-language effect. He ends the chapter by describing a spoken word recognition model for bilinguals that accounts for the effects found.

The author’s Complementarity Principle states that bilinguals usually acquire and use their languages for different purposes, in different domains of life, with different people. Different aspects of life require different languages. The author first evokes the contribution of past research on his thinking about the topic. For instance, early sociolinguistic studies of bilingual communities put heavy emphasis on the functions of languages. He then concentrates on the principle itself as it slowly came into focus in his work. He defines it, presents it in a diagram, and discusses its impact on language proficiency, dominance, and translation abilities in bilinguals. This is followed by a description of studies undertaken in his laboratory that found evidence for it, as well as his search for studies in production, perception, and language acquisition that confirmed its importance. The author then discusses the coming of age of the principle reflected in the reactions of researchers in the field, and the various studies, mostly experimental and descriptive, they have conducted to examine it. The principle is one of the most pervasive aspects of individual bilingualism, and it is invariably present in bilingual psycholinguistic research as an independent, control, or confounding variable.

At the start of his career, the author was struck by the many questionable conceptions and negative attitudes that surrounded bilingualism. He addressed them in two theoretical papers, in 1985 and 1989, in which he argued that a fractional view of bilingualism had played too great a role in the field. He then expressed his own holistic view that bilinguals are not two monolinguals in one person. Instead, they are an integrated whole which cannot easily be decomposed into two separate parts. Bilinguals have a unique and specific linguistic configuration; the coexistence and constant interaction of the two languages has produced a different but complete language system. After expanding on this, the author adds a few follow-up comments to complement his view. They concern the definition of bilingualism, the language history of bilinguals, the difference between monolinguals and bilinguals, and so on. The author ends by summarizing the impact his holistic view has had over the years on theories and models of bilingualism, as well as on the use of tranlanguaging in schools, and the learning and evaluation of foreign languages.

The author has always shown interest in bilinguals who are also bicultural – also known as bicultural bilinguals. In this chapter, he concentrates on the bicultural component of these bilinguals: they take part, to varying degrees, in the life of two or more cultures; they adapt, at least in part, their attitudes, behaviors, values, languages, and so on to these cultures; and they combine and blend aspects of the cultures involved. He then evokes how one becomes bicultural and how biculturalism evolves over time. This is followed by his proposal to adapt the language mode concept to account for how biculturals modify their behaviors in different situations. Biculturals find themselves at various points along a situational continuum – cultural this time – that requires different types of behavior and attitudes depending on the situation. At one end they are in a monocultural mode, and at the other end they are in a bicultural mode. The last two sections concern bicultural identity and the question of whether bicultural bilinguals change personality when they change language.

The chapter covers special bilinguals; that is, those who have both a regular and a unique relationship with their languages. Among them, one finds bilingual writers of literature who express their art in their first language, their second or third language, or even in both their languages. There are also those who make a living from their extensive knowledge and careful use of their languages such as interpreters, translators, second-language teachers, and so on. Others, such as airline pilots and traffic controllers, or foreign correspondents, do not have to reflect on the linguistic aspect of their languages as much but depend on them, as well as on specific skills, to do their jobs. And others still owe a lot to their language proficiency and bicultural abilities to assure their safety, such as sleeper agents. All share many similarities with regular bilinguals, but they are also characterized by a number of interesting differences. The author concentrates on the latter.

Bilinguals change their way of communicating when they are with monolinguals and when they are with bilinguals who share their languages. Whereas they avoid using their other language(s) with monolinguals (they are in a monolingual mode), they may call upon it (or them) when interacting with bilinguals, either by changing over completely to the other language(s) or by bringing elements of the other language(s) into the language they are speaking (they are then in a bilingual mode). The author reviews how he developed the notion of language mode, which, at the cognitive level, implies a change of activation of the languages and processing mechanisms. He summarizes some of the basic elements of language mode as described in a 2001 seminal chapter, discusses how language mode has fared since, and presents additional evidence for it. He then proposes some follow-up comments that deal with the level of activation of the deactivated language(s) in a monolingual mode, the complex nature of the variable that is language mode, and how it compares to the adaptive control hypothesis. He ends with reactions to language mode – many positive and some critical.

The influence of one language on the other when bilinguals speak and write monolingually is an intriguing phenomenon. The author first revisits how interference has been defined over the years by major researchers. He then argues that the definitions proposed were simply too broad, and covered not only interferences but also other contact phenomena such as code-switches and borrowings. The only way to get to the bottom of this problem is to control the language mode bilinguals and language learners are in when they are being observed. In addition, he suggests that we differentiate permanent traces of one language on the other (to be called transfers) from ephemeral intrusions of the other language (these would be interferences). The author continues by describing research conducted with his colleagues on Spanish–French bilinguals in the French-speaking part of Switzerland. The results obtained allowed them to have a better understanding of language restructuring in a first language. In addition, and as a by-product, it gave them a way to differentiate ephemeral intrusions from more permanent traces of the other language. He ends the chapter with a few words on bilinguals’ comprehension of speech containing cross-linguistic influences that comprise both transfers and interferences.

This chapter has three parts. In the first, the author concentrates on the deaf bilingual and explains what it means to be bilingual in sign language and the spoken (majority) language. Similarities with hearing bilinguals as well as differences are discussed. In the second part, he examines the biculturalism of deaf people: like hearing biculturals, they take part, to varying degrees, in the life of two worlds (the deaf world and the hearing world), they adapt, in part, their attitudes, behaviors, values, languages, and so onto both worlds, and they combine and blend aspects of the two. He also discusses cultural identity among deaf and hard-of-hearing persons. And in the third part, the author considers the deaf child and why it is so important for him/her to be able to grow up bilingual in sign language and the spoken language. He points to the role of both languages and argues that pursuing solely an auditory/oral approach puts the child at risk cognitively, linguistically, and personally. He ends by examining the reactions his writings have had on the field, and concludes with a few final remarks.

The careers of academics are rather straightforward, but since research on bilingualism and biculturalism have potentially important social consequences, the author communicated about them. His audience was the general public as well as professionals involved with bilingual children and adolescents. In this chapter, he describes three activities he undertook over the years. The first was to write books and articles, and give interviews, on the myths that surround bilingualism as well as on topics such as its extent, how it can be defined, having an accent in one or several languages, the personality of bilinguals, how children go in and out of bilingualism, family strategies to ensure that children become bilingual, and so on. The second activity was to have a blog on bilingualism, “Life as a Bilingual,” which was housed by a well-known social media organization, Psychology Today. The author maintained it for eleven years and it has been visited by more than 2.4 million readers. And the third activity was to defend the right of the deaf child to grow up bilingual. He wrote a position paper, which has been translated into 31 different languages. Reactions to these activities are then reviewed and discussed.

National censuses are rarely interested in those who know and use two or more languages, and they seldom make available statistics that reflect the bi- or multilingualism of their population. The author recounts how, over the years, he researched how many bilinguals there are in various countries. He contacted national statistical offices and census bureaus, studied their data, and perused national and transnational reports. He also interacted with official statisticians, who answered his questions and sent him unpublished data. And sometimes he went on specific quests to hunt down particular numbers or percentages that were being passed around. Here he concentrates on the results he obtained for the United States, Canada, Switzerland, and France. He ends with the holy grail many have been searching for – the proportion of bilinguals in the world. He gave an estimate back in 1982 – about half of the world’s population – and discusses how, with time, even 65 percent was proposed by some. Understanding why that was so was an adventure in its own right.

The author’s interest in bilinguals and bilingualism was triggered by his own bilingualism. He started on his journey in languages and cultures at the age of eight in English schools, first in Switzerland and then in England. During those ten years, he often reflected on what it means to use two or more languages in everyday life. This led him to do a Master’s thesis on bilingualism at the Sorbonne with Dounia Fourescot-Barnett. He wanted to find out about the topic and, indirectly, better understand what he was going through linguistically. A few years later, after having moved to the United States, he surveyed the field for his first book on bilingualism, Life with Two Languages. The book was organized from the macro to the micro level in six chapters: “Bilingualism in the World,” “Bilingualism in the United States,” “Bilingualism in Society,” “The Bilingual Child,” “The Bilingual Person,” and “Bilingual Speech and Language.” The book was one of the first-generation books on bilingualism that surveyed the field as it stood at the time. It was at that time that the author met Einar Haugen who befriended him and encouraged him to undertake research in the field.