This article begins with an examination of definitions of family firms. The debate about what constitutes a family firm is every bit as complex as the definition of an entrepreneur. This article explores the range of definitions but shows that any definition needs to be interpreted in its economic, social, institutional, and cultural context. An explanation for the multiplicity of definitions is provided in in this article, which explores the diversity in scale, scope, organization, and longevity of family firms, and shows differences through time in different societies and between families. The article also demonstrates the strong path dependency of family firm development, with change (or lack of it) underpinned by the foundations of the past. The article further explores research which compares the performance of family firms with non-family firms and this highlights the potential policy implications of family business research.