The Great Backyard Bird Count is an annual four-day event that engages bird watchers of all levels in counting birds and reporting their results to create a mid-winter snapshot of the numbers, kinds, and distribution of birds across the continent. Participants count birds for as little or as long as they wish during the four-day period and tally the highest number of birds of each species that they see at any one time. At the Great Backyard Bird Count web site, they fill out an online checklist to submit their counts.

As the count progresses, anyone with Internet access can explore what is being reported from their own towns or anywhere in the United States and Canada. They can also see how the current year's numbers compare with those from previous years. Participants may also send in photographs of the birds they see. A selection of images is posted in the GBBC online photo gallery.

After the count, scientists analyze the results and post summaries highlighting the year's trends and findings.