Sibling ties in adulthood are extremely diverse. They vary by genetic relatedness, by structural features (such as ordinal position and number of siblings), and by siblings' biological and legal relationship. Nonetheless, siblings have commonalities, including the lifelong adverse effects of parental favoritism on their relationship and the importance of egalitarianism in their exchanges of support. Compared to friends, affection is more important for exchange of support to occur, and it is siblings' differences, not similarities, that tend to promote these exchanges. Cultural variations are noteworthy; Filipino American siblings stay more in contact and have less conflict than any other siblings in the United States. Some cultures, such as Korean, have witnessed radical changes in the sibling relationship over time. Interventions are needed throughout life that promote sibling affection and support in later life.