Answer
Globally, there are 28 countries that have some form of bicycle helmet requirement (see Figure 1; [9]). Sometimes helmets are mandatory for all cyclists, sometimes only for children or young people, sometimes only in certain situations.
- For everyone, everywhere: in Argentina, Australia, Chile, Finland, Japan, Malta, Namibia, New Zealand, Nigeria, Slovakia, United Arab Republics, South Africa and in some provinces/states of Canada and the United States;
- For children/young people (between up to 12 and up to 18 years old), everywhere: in Estonia, France, Iceland, Israel, Jersey, Croatia, Latvia, Lithuania, Austria, Slovenia, Spain, Czech Republic, South Korea, Sweden, some Canadian provinces and some US states;
- Situation-dependent: for adults in Israel and Spain only on roads outside urban areas, except - in Spain - when cycling uphill.
Not all countries impose fines if cyclists do not wear helmets; for example, Finland and Japan do not impose fines.

Figure 1. Countries where bicycle helmets are mandatory for at least some age groups. Source: [9].