This article serves as a state-of the-science review of the blossoming field of generative third language (L3) acquisition as well as an introduction to this special issue on the same topic. We present and argue for the relevance of adult L3/Ln acquisition for many perennial questions that have sat at the core of linguistic approaches to adult language acquisition since the Principles and Parameters framework was first adopted into second language acquisition (SLA; e.g. Flynn, 1985, 1987; Liceras, 1985; White, 1985a, 1985b; Schwartz, 1986). Furthermore, we highlight the unique, specific questions that have emerged from studying L3/Ln from a generative perspective thus far while suggesting refinements to these questions and additional ones that should emerge in future inquiry.