What is the basis of our ability to assign meanings to words or to objects? Such questions have, until recently, been regarded as lying within the province of philosophy and linguistics rather than psychology. However, recent advances in psychology and neuropsychology have led to the development of a scientific approach to analysing the cognitive bases of semantic knowledge and semantic representations. Indeed, theory and data on the organisation and structure of semantic knowledge have now become central and hotly debated topics in contemporary psychology.This special issue of Memory brings together a series of papers from established laboratories that are at the forefront of semantic memory research. The collection includes papers presenting theoretical overviews of the field as well as papers containing new experimental findings. A variety of approaches to the problems of analysing semantic knowledge and semantic representations are included in this volume. For example, experimental studies of normal subjects are included together with neuropsychological investigations of patients with impaired semantic memory and computational models of the representation of knowledge in normality and disease. This collection will therefore be essential reading for researchers and others who are interested in memory function. It will also be of interest to cognitive scientists, linguists, philosophers and others who have puzzled over the many complex and central questions that probe the roots of our ability to understand meaning.