The complexity of defining what or who constitutes a family is well known. With increasing variability in family structure and type over time, the idea of achieving a single, workable definition appears elusive for researchers, service providers and policy-makers alike. One view, proposed by Families Australia, cuts through these debates to suggest that families are what individuals define them to be. As such, family can be a fluid concept that may have markedly different meanings to different individuals, even those living under the same roof. This article explores some of the many approaches to defining families, as well as providing an overview of the feature articles in this edition of Family Matters.