This edited volume presents unique insights on sibling relationships in adulthood in the early 21^st century, focusing on three themes: relations beyond childhood and school years; factors shaping social support provision between siblings; and changes in family life and how these impact sibling relations. Comprised of chapters from distinguished international family scholars, this book examines sibling dynamics across age, race, culture, gender, sexual orientation, geography, and social environments. It answers important questions such as, to what extent do siblings support each other at different stages of the life cycle? How do cultural practices and family obligations impact on sibling support? How does sibling support differ when looking at surrogates, migrant families, polygamous families, and siblings with disabilities?