Although bicycle speed is rather limited, it is acknowledged that a properly designed helmet provides very good protection for the most vulnerable part of the body, the head, from being severely injured in a crash. Whereas the helmet is more or less compulsory in all countries for participants in sporting events, in most countries it is still optional for cycle touring or bicycle rides in general (see Bicycle helmet legislation for exceptions). Some cyclists are against the helmet as it imposes a requirement conflicting with the feeling of freedom given by the bicycle or because it is unsightly, uncomfortable, or unnecessary over short distances. Others are firmly in favour of it as it provides good head protection .
In 2000, helmets were worn on a voluntary basis by 15% of cyclists in Finland, 16% in the United Kingdom, 17% in Sweden, 7% in Switzerland and 6% in Norway. In Denmark, 68% of children, who are passengers on bicycles (children between 0 and 5 years old), were using helmets. 34% of the children between 6 and 9 years old use helmets on their bicycles. Only 5% of cyclists aged between 10 and 25 year old used a helmet, and among cyclists aged 25 years and older only 3% used a helmet. The proportion is insignificant in most other countries .
Several reviews have been conducted on the effectiveness of bicycle helmets in reducing head and facial injuries . Studies over the last 15 years in the United States, Europe, Australia and New Zealand indicate that bicycle helmets are very effective in decreasing the risk of head and brain injuries. Critics of legislation, though, have pointed out that reductions in absolute numbers of cycling fatalities and severe head injuries can be at least partially explained by a decrease in cycling per se. Given that good evidence exists that regular cycling is associated with considerable health benefit, and that the benefits heavily outweigh the risk of injury, there is understandable concern about legislation resulting in a reduction of cycling levels.
Additionally, there is a broader debate about whether helmet use is the best way to improve the safety of cyclists. An alternative approach to this issue is adopted in the Netherlands. The Dutch government, private safety organizations and cyclists' groups all tend to agree on the following propositions: Promoting the use of bicycle helmets runs counter to present government policies that are aimed at the primary prevention of crashes (as opposed to secondary prevention) and at stimulating the use of the bicycle as a general health measure. Attempts to promote bicycle helmets should not have the negative effect of incorrectly linking cycling and danger. Nor should the promotion of helmets result in a decrease in bicycle use. Because of these considerations, a mandatory law for bicycle helmet use has not been thought an acceptable or appropriate safety measure in the Netherlands .
Towner et al.  have summarised the pros and cons of bicycle helmet legislation as follows:
- The pro-bicycle helmet group base their argument on the fact that there is scientific evidence that, in the event of a fall, helmets substantially reduce head injury.
- The anti-helmet group base their argument on several issues including: compulsory helmet wearing leads to a decline in cycling, risk compensation theory negates health gains, scientific studies are defective, and the overall road environment needs to be improved.