The gray wolves at Yellowstone were caught in the wild in Canada and flown to the Park and released. Technically this wasn't actually a reintroduction. When we capture wild animals and release them in a new area, this is called a "translocation" (trans-low-CAY-shun).
The red wolves released at Alligator River National Wildlife Refuge, North Carolina, in 1987 were the first wolves to be actually "reintroduced" to the wild successfully. The first group of red wolves to be released were born in captivity. Prior to their release they had never set foot outside their pens and had never killed a prey animal. Despite their lack of wild experience, the first red wolves did quite well. They learned to hunt and kill prey, how to find their way in the woods, and perhaps most importantly, how to stay away from people.
Why release wolves into the wild?
Another reason for releasing wolves into the wild is to protect habitat. In the United States, outside of national parks and refuges, we don't have specific laws protecting habitat. But we do have a law called The Endangered Species Act. This powerful law helps protect animals and plants that are threatened with extinction. When we release a wolf into the wild, the endangered species laws protecting the wolf help to protect the habitat the wolf is living in.
Yet another good reason for reintroducing wolves is economic. It has been proven that wild wolves bring in millions of dollars from tourists traveling to parks, refuges, and wilderness areas that have wolves. These "tourist dollars" provide jobs for people living in cities and towns near the wild places where wolves live.