Sometimes the only difference between a bad motorcycle injury and certain death is your helmet. We can go into the all the reasons why wearing a motorcycle helmet should not be regulated by the government (civil liberty rights, freedom of expression, etc.) but the fact remains is that 47 out of the 50 states have motorcycle helmet laws.
Know your state and the laws that pertain to wearing helmets. Only three (3) states are on the books today with no laws- Illinois, Iowa and New Hampshire. All other states require that if you are under 18 you must wear a helmet. Over 18 years of age, it will be different by state as to whether or not the driver needs to wear a helmet. In the majority of states, if you have a passenger, the passenger is required to wear a helmet. Helmets must meet D.O.T. (department of transportation) qualifications. Check with your local bike--- and no your bicycle helmet will not qualify as a motorcycle helmet!