* This state-of-the-art text reviews, evaluates, and reflects on L2 development across the lifespan as a complex variable that is both socio-cultural as well as maturational in nature - with a chronological chapter lineup from infant bilinguals to L2 learners in adolescence, adulthood, and older age. * Offers in-depth discussion of highly pertinent yet underresearched topics, like L2 learners in older individuals, as well as an innovative chapter on L2 learning in the context of cross-cultural/binational/plurilingual romantic relationships, in both cases with diverse circumstances, motivations, and outcomes. * The first book taking on this area in its fullness and in a way accessible to students and non-specialist - with a concerted, authored text. Previous works are focused on one age cohort, edited volumes rather than unified authored books, and the most closely competing books were published over a decade (and sometimes over three decades) ago.