Bran the Builder gave the land up to twenty-five leagues south of the Wall to the Night's Watch for their "sustenance and support." Jon Snow agreed to allow Stannis Baratheon to settle wildlings on the Gift following the Battle of Castle Black. 
The New Gift
Thousands of years later when Queen Alysanne came to the North she visited the Wall. She held the Night's Watch in great esteem and convinced her husband Jaehaerys I to double the land, extending it out a further twenty-five leagues, which was called the New Gift. The villages that existed on the New Gift payed their taxes in goods and labor to the Night's Watch, helping feed and provide food for the brothers.
References and Notes