In this chapter, we reinforce the book’s aim to shed light on changes inflicted on language, cognition, and the brain rather than to focus on advantages and disadvantages of being bilingual. To obtain a more realistic picture of bilingualism, its assets (i.e., what is easier), and its difficulties (i.e., what is taxing and leads to high consumption of mental resources), we have drawn on research from various disciplines. We conclude the book by identifying complexity as the major issue for research on bilingualism. The complexity problem is fundamental to definitions of bilingualism and the characterization of bilingual participants in empirical studies, leading to discussions about its assessment as a dichotomous or continuous variable. Considering bilingualism as an experience and how such experience impacts overall language development, cognition, and the brain at different levels are related to usage-based approaches of examining bilingualism as well as a concern regarding confounding and moderating variables. The shift for designing research in the field of bilingualism seems to necessarily be more interdisciplinary in nature than in the past.

The concept of accommodative coping refers to a "family" of processes by which goal blockages, losses, and similar threats to quality of life are coped with by adjusting individual goal and valuation structures, i.e., in particular by devaluing or "letting go" of threatened or blocked goals and upgrading and pursuing alternative, more attainable goals in their place. While the functionality of accommodative regulatory processes in older and older adulthood has long been elaborated theoretically in several compatible modeling approaches and well studied empirically, accommodative processes in childhood and adolescence have only recently attracted scientific attention. It is helpful here to distinguish the efficacy of accommodative processes in childhood and adolescence itself from the developmental conditions for accommodative processes in adulthood and old age. Combining these perspectives opens up the prospect of an actual lifespan perspective on developmental regulation.