小约翰·赫歇尔·格伦（John Herschel Glenn Jr.，1921年7月18日－）曾是一位美国国家航空航天局的宇航员，执行过水星-大力神6号以及STS-95任务。格伦是第一个进入地球轨道的美国宇航员。

格伦出生于俄亥俄州的坎布里奇，到附近的马斯金格姆学院上学，然后参加了美国海军的一个飞航训练项目。他在第二次世界大战和朝鲜战争期间是战斗机驾驶员。1954年，他完成了试飞员的训练。1957年，格伦上校驾驶超音速飞机进行了人类第一次跨大陆无间歇飞行。

1959年，他是美国最初被选为宇航员的7个人之一。1962年2月20日，格伦在狭窄的友谊7号宇宙飞船中环绕地球飞行了三圈，然后安全降落在海面上。那次飞行持续时间不到5个小时，使他成为环绕地球飞行的第一个美国人。

John Herschel Glenn, Jr. (born July 18, 1921), (Col, USMC, Ret.), is a former Marine Corps aviator, engineer, astronaut, and United States senator. He was selected as one of the "Mercury Seven" group of military test pilots selected in 1959 by NASA to become America's first astronauts and fly the Project Mercury spacecraft. On February 20, 1962, Glenn flew the Friendship 7 mission and became the first American to orbit the Earth and the fifth person in space, after cosmonauts Yuri Gagarin and Gherman Titov and the sub-orbital flights of Mercury astronauts Alan Shepard and Gus Grissom. Glenn is the earliest-born American to go to orbit, and the second earliest-born man overall after Soviet cosmonaut Georgy Beregovoy. Glenn received the Congressional Space Medal of Honor in 1978, and was inducted into the U.S. Astronaut Hall of Fame in 1990. With the death of Scott Carpenter on October 10, 2013, Glenn became the last surviving member of the Mercury Seven.