This book draws upon innovative qualitative data sources to explore the significance of siblings throughout the life course, demonstrating why sociologists ought to pay attention to siblingship. Focussing on four themes central to the discipline of sociology - self, relationality, imagination and time - the book shows why siblings matter. Grounded in theories of relatedness but spanning theoretical work on generation, life course, emotion, sensory worlds, normativity and identity, Siblings and sociology explores the importance of siblings in everyday life and how they inform wider social processes: the relational construction of identity, the inculcation of capital, experiences of institutions like schools and the meanings of relatedness. Siblings tap into profound questions about who we are and who we can become. This book shows how the intrigue of siblingship renders them an important lens through which to think in new ways about familiar sociological ideas.