This volume brings together ten contributions to the study of untutored (mainly) second but also first language acquisition. All chapters have been written from a functionalist perspective and take as the main theoretical framework a model of spontaneous second language acquisition centered on the "basic variety" as proposed by Klein and Perdue. The chapters in the volume are grouped around two research themes. The first theme concerns the acquisition of scope phenomena (negation, scope particles), the second one deals with referential movement (reference to person, time and space). Both parts provide insights in the structure of learner varieties at various stages of development, and are followed by a discussion chapter.