For learners to become competent speakers of a language, they have to learn the inventory of morphosyntactic constructions in the language and use them in pragmatically appropriate ways (mapping universal pragmatic principles onto language specific structures, selecting only those options that are syntactically possible). Taking into account that languages vary in the way discourse notions such as TOPIC and FOCUS are mapped onto syntactic structures, a study of the syntax-pragmatics interface is relevant for L2 acquisition. This study of French and Spanish L2 learners of different proficiency levels investigates various syntactically and/or pragmatically challenging structures related to argument realization (i.e. subjects and objects) in the light of and to advance current research in the field. It (1) evaluates whether syntax-pragmatics interface phenomena are vulnerable (acquired late and/or difficult to acquire), and (2) tests whether the syntax-pragmatics interface exhibits more developmental instability than narrow syntax. This book should be useful for linguists, foreign language teachers and or anyone interested in learning more about L2 acquisition of French or Spanish.