One of the joys of visiting the Netherlands is that I always ride without a helmet there. The bike I ride there is more of an upright model and the infrastructure is very much designed around bicycles. Here in the U.S., I wear a helmet when riding my road bike. With my commuter bike, it varies. A few blocks to the store, I may not wear the helmet. More than that, I generally do. My thinking around this has evolved. While accidents are always possible, I don't think riding a bicycle at a commuter speed is inherently dangerous. Even as a pedestrian, I can step off the curb funny and trip & bang my head or break an ankle. I don't judge others in the U.S. for riding with or without, other than kids. IMO, children should always wear helmets (mine did) as they just don't have the coordination and judgment yet that experienced adult riders have. And with the hills around here, kids can pick up speed very quickly.