The American Tree Farm System (ATFS) is the largest and oldest woodland certification system in America. It is internationally recognized by the Programme for the Endorsement of Forest Certification and meets strict third-party certification standards. It is one of three certification systems currently recognized in the United States (the others include the Forest Stewardship Council and the Sustainable Forestry Initiative). ATFS specializes in certifying private forests, primarily those held by individuals and families and currently certifies over 24 million acres (110,000 km²) of forestland. The ATFS Standard for Certification is owned by the American Forest Foundation, a national nonprofit organization focused on promoting sustainable stewardship of America's woodlands and related environmental education through Project Learning Tree.