Walter Tennyson Swingle (January 8, 1871–January 19, 1952) was an American agricultural botanist who was born in Canaan, Pennsylvania and moved with his family to Kansas two years later. He graduated from the Kansas State Agricultural College in 1890, and studied in Bonn in 1895-96 and 1898. He worked at the United States Department of Agriculture (1891), investigated subtropic fruits, established laboratories in Florida, became an agricultural explorer, and (after 1902) had charge of crop physiology and breeding investigations. He made several visits to the Mediterranean countries of Europe, to North Africa, and to Asia Minor, from where he introduced the date palm, pistache nut, and other useful plants, and also the fig insect to make possible the cultivation of Smyrna figs in California. He also traveled to Asia, bringing back 100,000 Chinese volumes on botany to the Library of Congress. With Webber, he originated citranges, a hardy citrus fruit.
Swingle married Lucie Romstaedt in 1901; she died in 1910. He married Maude Kellerman in 1915.