William S. Arnett (born May 10, 1939) is an Atlanta-based writer, editor, curator and art collector who has built internationally important collections of African, Asian, and African American art. Arnett is the founder and Chairman Emeritus of the Souls Grown Deep Foundation, an organization dedicated to the preservation and documentation of African American art from the Deep South that works in coordination with leading museums and scholars to produce groundbreaking exhibitions and publications using its extensive holdings. He has exhibited works from those collections and delivered lectures at over 100 museums and educational institutions in the United States and abroad. He is perhaps best known for writing about and collecting the work of African American artists from the Deep South. Arnett was named one of the "100 Most Influential Georgians" by Georgia Trend Magazine in January 2015. 
Arnett was born in Columbus, Georgia, and attended the University of Georgia, where he earned a B.A. in English.
After living in Europe in the mid 1960s, Arnett built an extensive collection of ancient Mediterranean art and antiquities. He also became interested in Asian art, and amassed works dating from 2000 B.C. to the 19th century.
For a number of years, Arnett's main interest was African Art. He collected the ritual arts from West and Central Africa, particularly the numerous cultures of Nigeria, Benin (formerly Dahomey), the Cameroon Grassfields, and the Democratic Republic of the Congo. In 1978, he co-authored the catalogue Three Rivers of Nigeria for Atlanta's High Museum of Art. In 1994, he donated a significant portion of his extensive collection of African art to the Michael C. Carlos Museum at Emory University, then under the direction of Maxwell Anderson.
In the mid 1980s, Arnett began to collect the work of artists in the black American South, including pieces by such artists as Thornton Dial and Lonnie Holley. By the mid-1990s Arnett’s efforts resulted in an ambitious project to survey the visual tradition of the African American South: an exhibition and two-volume book, titled Souls Grown Deep: African American Vernacular Art of the South, which was ultimately presented at the 1996 Olympic Games in Atlanta and remains the most in-depth, scholarly examination of this phenomenon. Subsequently, Arnett developed a series of related publications, including several books on the quilts created by women living in Gee's Bend, Alabama. He arranged for the first influential exhibition of those quilts at the Museum of Fine Arts, Houston in 2002. The exhibition titled The Quilts of Gee's Bend was shown at 13 major US museums including the Whitney Museum of American, the High Museum of Art, MFA Boston, the Milwaukee Museum of Art, the Cleveland Museum of Art, the Corcoran and the deYoung Museum, and the High Museum of Art.
On November 24, 2014, The Metropolitan Museum of Art announced that 57 works by contemporary African American artists from the Southern United States were donated to the Museum by the Souls Grown Deep Foundation from its William S. Arnett Collection. An exhibition devoted to the gift will take place at the Metropolitan Museum in fall 2016.
As Sheena Wagstaff, Leonard A. Lauder Chairman of the Department of Modern and Contemporary Art at the Metropolitan Museum, described the gift, “From Thornton Dial’s magisterial constructions to the emblematic compositions by the Gee’s Bend quilters from the 1930s onwards, this extraordinary group of works contributes immeasurably to the Museum’s representation of works by contemporary American artists and augments on a historic scale its holdings of contemporary art.” 
As Arnett's collection of African American art grew, he became convinced that the so-called folk or outsider artists of the black American South were a coherent cultural movement and constituted a crucial chapter in world art. He spent years gathering extensive documentation and amassing a near-definitive collection of work crucial to the understanding of this cultural phenomenon.
In an effort to introduce southern black vernacular art to a wider audience, Arnett founded Tinwood Books with Jane Fonda. Under the Tinwood imprint, he edited and co-authored Souls Grown Deep: African American Vernacular Art of the South, a massive book that featured over 1800 illustrations and ran to over 1000 pages in two volumes. An exhibition of the same title was presented at the 1996 Olympic Games in Atlanta. Additionally, Arnett has edited and/or co-authored many other books, including Gee's Bend: The Women and Their Quilts, Gee's Bend: The Architecture of the Quilt, and Thornton Dial in the 21st Century.
- "Souls Grown Deep Foundation".
- "Michael C. Carlos Museum-African Art Collection". Emory University. Retrieved 14 September 2011.
- "Souls Grown Deep and the Cultural Politics of the Atlanta Olympics". Radical History Review (98). Spring 2007. pp. 97–118.(subscription required)
- Wallach, Amei. "Fabric Of Their Lives". Smithsonian Magazine. Retrieved 14 September 2011.
- "Souls Grown Deep Foundation". Retrieved 14 September 2011.
- Sellman, James. "Truth and Consequences: The 25-Year Friendship of Thornton Dial and Bill Arnett". Folk Art Messenger. Folk Art Society of America.