This chapter examines Generative Second Language Acquisition (GenSLA). The central tenet of generative grammar posits that humans possess an innate language faculty, which enables them to acquire language and develop unconscious knowledge that extends beyond the input provided—a concept often referred to as the logical problem of language acquisition. The theory of this innate biological component is called Universal Grammar (UG), which is considered relevant to first-language acquisition and second-language acquisition (SLA). GenSLA investigates whether UG constrains interlanguage representations and, if so, to what extent and in what ways. The chapter reviews the role of UG in SLA and explores key phenomena such as wh-movement, pronominal binding and the (un)availability of formal features. It concludes that the GenSLA findings partially apply to textbooks and explicit instructions.