What makes a child's language development trajectory have the patterns that it has, and what causes differences across children in those patterns? These fundamental questions have for over half a century been at the heart of research on language development in monolingual children, on the cross-linguistic development of language in children from distinct language communities, on bilingual language development, and on development in cases of language disorders in children. Paradis has taken the important step of carefully comparing the trajectories of two populations of children--children with specific language impairment (SLI) and children growing up bilingually--who both differ in interesting ways from normally developing monolingual children. Her Keynote Article highlights striking similarities and potential differences between these two groups. This Commentary focuses on three issues: what influences developmental profiles in language development, bilinguals' development of vocabulary and syntax, and assessment issues related to treating monolinguals as the "standard."