Linking recent advances in theoretical syntax and empirical research in language development, the book claims that second language acquisition is not totally distinct from first language acquisition, but rather is a replay, a relearning of language. It argues that Universal Grammar is a template guiding acquisition of L1 while constraining acquisition of L2. Assuming that a syntactic distinction crucial for language and its acquisition is the division between lexical and functional categories, it argues that the key to L2 as well as L1 acquisition of syntax is the mastery of morphological features and their linking to functional categories. It thus supports the availability of UG to the second language learner and the minimalist claim that cross-linguistic variation is morpholexical. Constructionism, the hypothesis of L2A proposed in this account, argues for a period of feature underspecification after loss of the L1 value, followed by a progressive building of the L2 value through specific constructions.