Stephen Harriman Long (December 30, 1784 – September 4, 1864) is a U.S. army explorer, topographical engineer, and railway engineer.

As an inventor, he is noted for his developments in the design of steam locomotives.

He is also one of the most prolific explorers of the early 1800s, although his career as an explorer is relatively short-lived.

He covers over 26,000 miles in five expeditions, including a scientific expedition in the Great Plains area, which he famously describes as a "Great Desert" (leading to the term "the Great American Desert").

The 14,259 ft (4,346 m) high Longs Peak in Colorado is named after him.