U.S. state flag consisting of a dark blue field (background) bearing the name of the state and its official seal.

On March 5, 1866, Idaho Territory adopted its first official seal, representing mountains below a new moon, a steamer on the Shoshone River, figures of Liberty and Peace, an elk's head, and agricultural produce. A similar seal, with a rising sun replacing the moon and a miner instead of Peace, was adopted for the new state on March 14, 1891, and appears today in the state flag. The 1891 state seal is the only such American design to have been created by a woman, Emma Edwards (later Emma Edwards Green).

Idaho's first state flag, adopted by the legislature on March 12, 1907, was conceived as a simple blue field bearing the name of the state. A representation of the seal was subsequently added by C.A. Elmer, a brigadier general in the National Guard. The design then conformed to the general pattern of state flags, which were based on regimental colours of the Union army during the Civil War. Elmer's design was legalized on March 15, 1927, and a standard pattern for the seal was adopted in March 1957.