The M26 Adrian helmet (French term: "Casque Adrian") was a military helmet issued to the French Army during World War I. It was designed when millions of French troops were engaged in trench warfare and head wounds became a significant proportion of battlefield casualties.

The helmet was intended to protect the soldier from artillery shell shrapnel from above, hence the deflector crest. Like most helmets of this era, it was never designed to protect from the direct impact of rifle or machine gun bullets. It was made of mild steel and weighed only .765kg (1lb.11oz.) which made it lighter than the British Brodie helmet and the German Stahlhelm. More than three million Adrians were produced, and they were widely adopted by other countries including Italy, Belgium, Thailand and Russia. The Soviet model with a large red star became a classic symbol of the frontline soldier of the USSR (see figure.)

In the French army the Adrian helmet was standard military issue until after World War II, and was also used by the French police up to the 1970s. This helmet design was adopted by other countries such as Mexico. Adrian helmets are still prized by collectors today.

Propaganda poster featuring a Soviet soldier wearing the Adrian helmet with red star insignia