Recent data indicate that the average relationship duration for same-sex couples is just under 13 years. This entry provides details on the experiences of long-term (roughly defined as 5 years or longer) same-sex couples by presenting information on (1) demographic characteristics of same-sex couples in the United States; (2) families of same-sex couples; (3) relationship quality and relationship dynamics in long-term same-sex couples; (4) relationship stability and dissolution; (5) same-sex relationships and health; and (6) some of the unique challenges faced by aging same-sex couples, particularly in relation to health.