Citizen science is when regular people help scientists study the world. Citizen scientists usually collect information and send it to a team of scientists, who examine and process it. Most citizen scientists are volunteers and do not get paid.

Sometimes scientists ask for help from people who are collecting information anyway. For example, scientists studying birds might ask birdwatchers to record which birds they see and hear and then tell the scientists. The National Audubon Society has been running a Christmas Bird Count since 1900.