This volume consists of a collection of papers that focus on structural/grammatical aspects of the process of first language attrition. It presents an overview of current research, methodological issues and important questions regarding first language attrition. In particular, it addresses the two most prominent issues in current L1 attrition research: Can attrition effects impact on features of core syntax, or are they limited to interface phenomena?, and; What is the role of age at onset (pre-/post-puberty) in this regard? By investigating attrition in a variety of settings, from a case study of a Spanish-speaking adoptee in the US to an empirical investigation of more than 50 long-term attriters of Turkish in the Netherlands, the investigations presented take a new perspective on these issues.