The two basic questions in the field of language attrition are: why do people lose their language? and how do they lose their language? The former question concerns the factors which cause attrition, the latter the mechanics of the attrition process. Though the two questions are intimately related and mutually affect each other, this paper will draw upon two fields of research which are as yet largely unconnected to shed light on them. Where the why-question is concerned, it will argue for a perspective of developmental psychology in which developments over the whole lifespan are studied. The how-question, on the other hand, is best addressed within the framework of a dynamic systems perspective which focuses on the development over time of complex systems such as human cognition and language.