No. I saw three people riding these this morning on my 4 block walk to work and none of them were wearing a helmet. I have a personal rule though to always wear a helmet when riding a bike. On my monitor with the browser maximized, the bottom line of this page: http://citibikenyc.com/riding-tips says "Citi Bike encourages you to wear a helmet and never ever text while riding!" They also sent me a coupon for $10 off a helmet at local bike shops.