Adoption brings a child born to other parents into a new family. Birth parents have a number of reasons for placing children for adoption. In the end, it's usually because they want better lives for their children than they feel they can provide.
Children who are eligible for adoption come from many different settings. Some are in foster care, a temporary home setting. Other children live in orphanages or with birth relatives until they can be adopted.
There are different kinds of adoption. Whether the adoption is international versus domestic depends on whether a child is born in another country or born within the United States.
References and abstracts from MEDLINE/PubMed (National Library of Medicine)