This special issue explores the relevance of Dynamic Systems Theory (henceforth DST) to research in first language attrition (henceforth L1 attrition). While research in L1 attrition has traditionally drawn on paradigms in other areas of linguistic enquiry, e.g. approaches current in L2 acquisition studies, important developments across a range of disciplines have paved the way for a fundamentally different conceptualisation of language development. In this special issue, DST guides our enquiry into L1 attrition, which we view as one specific dynamic process of change in language development.DST was first linked to L1 attrition by Herdina and Jessner (2002), and then further developed by de Bot, who suggested that DST provides 'a fresh and promising perspective on language attrition as a normal part of language development and not as a lamentable loss of what once was' (2004, p. 233). De Bot argued that a DST-based model of language development should be applicable to language attrition and that the theoretical underpinning of L1 attrition research would be strengthened by adopting this perspective (see also Ecke, 2004). However, de Bot also pointed to methodological challenges implicit in applying a DST perspective to L1 attrition. Here, one of the most salient challenges is actually testing DST, a feat yet to be accomplished. Nevertheless, eight years on, the purpose of this special issue is to present for the first time empirical research which has adopted the DST framework to study L1 attrition across the lifespan.In this introduction, two propositions related to the relevance of DST in L1 attrition research are discussed.