Sibling relationships come in all shapes and sizes. A brief examination of families in literature demonstrates the diversity of sibling relationships. This chapter considers some of the factors that contribute to the dramatic individual differences in the quality of children's sibling relationships. It discusses sibling relationships from a developmental perspective, examining how the quality of children's relationships with their brothers and sisters changes from the preschool years to adolescence and beyond. The chapter explores the effects of gender, age gap and child temperament to investigate how sibling relationship quality may vary with characteristics of the sibling dyad and the children within it. Associations between temperament and relationship quality may also differ by gender: one study of school-aged sibling dyads found that the expected links between negative sibling behaviour and emotionality and activity only held true for sisters.