A helmet is a form of protective clothing worn on the head and usually made of metal or some other hard substance, typically for protection from falling objects or high-speed collisions. Helmets are common in the military, construction, mining and some sports, including American football and rock climbing. Motorcycle helmets and bicycle helmets are compulsory headgear in some jurisdictions; in the United Kingdom only Sikhs are allowed to ride motorcycles without wearing motorcycle helmets.

Helmets are among the most ancient forms of protection, and are known to have been worn by ancient Greeks and throughout the Middle Ages; at this time they were primarily military equipment, protecting the head from cutting blows with swords and flying arrows. They were initially constructed from leather, but eventually came to be made entirely from iron, with a variety of functional enhancements. Military use of helmets declined as firearms became widespread, where traditional helmets offered little protection. However, with the increasing use of heavy artillery, the steel helmet made a comeback in the 20th Century as protection for the head from shrapnel.

Goggles are another form of protective headgear. They are not typically needed while wearing a helmet that protects the eyes as well. Hard hats are typically preferred in modern times for construction workers.

See also:

• Adrian helmet
• Bascinet
• Brodie helmet
• Corinthian helmet
• Cervelliere
• Hard hat
• M1 Helmet
• PASGT "Fritz" helmet
• Pickelhaube
• Pith helmet (a.k.a. sun helmet)
• Sallet
• Stahlhelm
• Leather helmet