A motorcycle helmet is a type of helmet used by motorcycle riders. Motorcycle helmets contribute to motorcycle safety by protecting the rider's head in the event of an impact. They reduce the risk of head injury by 69% and the risk of death by 42%. Their use is required by law in many countries. However, only 10.4% of all Motorcyclists wear helmets, according to the World Health Organization in 2016.

Motorcycle helmets consist of a polystyrene foam inner shell that absorbs the shock of an impact, and a protective plastic outer layer. Several variations exist, notably helmets that cover the chin area and helmets that do not. Some helmets provide additional conveniences, such as ventilation, face shields, sun visors, ear protection, or a wireless microphone.^{[citation needed]}

The origins of the crash helmet date back to the Brooklands race track in early 1914, when a medical officer, Dr. Eric Gardner, noticed he was seeing a motor cyclist with head injuries about every two weeks. He got a Mr. Moss of Bethnal Green to make canvas and shellac helmets stiff enough to stand a heavy blow and smooth enough to glance off any projections it encountered. He presented the design to the Auto-Cycle Union where it was initially condemned, but later converted to the idea and made them compulsory for the 1914 Isle of Man TT races, although there was resistance from riders. Gardner took 94 of these helmets with him to the Isle of Man, and one rider who hit a gate with a glancing blow was saved by the helmet. Dr. Gardner received a letter later from the Isle of Man medical officer stating that after the TT they normally had "several interesting concussion cases" but that in 1914 there were none.

In May 1935, T. E. Lawrence (known as Lawrence of Arabia) had a crash on a Brough Superior SS100 on a narrow road near his cottage near Wareham. The accident occurred because a dip in the road obstructed his view of two boys on bicycles. Swerving to avoid them, Lawrence lost control and was thrown over the handlebars. He was not wearing a helmet, and suffered serious head injuries which left him in a coma; he died after six days in the hospital. One of the doctors attending him was Hugh Cairns, a neurosurgeon, who after Lawrence's death began a long study of what he saw as the unnecessary loss of life by motorcycle despatch riders through head injuries. Cairns' research led to the increased use of crash helmets by military and civilian motorcyclists and the British Army making helmets compulsory for its riders in November 1941.

In the Soviet Union, helmets for motorcyclists became mandatory in November 1967. Protective helmets for all motorcyclists and passengers became mandatory in January 1973.

A 2008 systematic study showed that helmets reduce the risk of head injury by around 69% and the risk of death by around 42%.

Although it was once speculated that wearing a motorcycle helmet increased neck and spinal injuries in a crash, recent evidence has shown the opposite to be the case: helmets protect against cervical spine injury. A study that is often cited when advancing the argument that helmets might increase the incidence of neck and spinal injuries dates back to the mid-1980s and "used flawed statistical reasoning".

There are five basic types of helmets intended for motorcycling, and others not intended for motorcycling but which are used by some riders. All of these types of helmets are secured by a chin strap, and their protective benefits are greatly reduced, if not eliminated, if the chin strap is not securely fastened so as to maintain a snug fit.