Amateur radio — also known as ham radio — is both a hobby and a public service practiced worldwide. During a natural disaster or other crisis, amateur radio can operate when cellphones and land lines cannot. During Hurricane Katrina, for example, more than 1,000 radio amateurs traveled to the Gulf Coast to provide emergency communications. When the Boston Marathon bombing overwhelmed cellphone service, hams provided much needed communications. The Red Cross dispatched 50 hams to help in Puerto Rico During Hurricane Maria in 2017.
In the United States, the Federal Communications Commission licenses amateur radio. The three classes of amateur are Technician, General, and Extra. Each class requires an increasing difficult written exam, but comes with additional privileges, such as access to more frequencies.