When: Officially the last Tuesday of February, with events and activities taking place throughout the month of February.

Where: Across the United States and U.S. territories.

Why: Four million cats and dogs—about one every eight seconds—are put down in U.S. shelters each year. Often these animals are the offspring of cherished family pets, even purebreds. Maybe someone's cat or dog got out just that one time or maybe the litter was intentional, but efforts to find enough good homes failed. Spay/neuter is the only permanent, 100-percent effective method of birth control for dogs and cats and a proven way to reduce the vast numbers of animals who are born only to die prematurely and without a family who loves them. Learn more about why you should spay or neuter your pet.

Meet the winners of the 2009 Spay Day Online Pet Photo Contest »

Watch a slideshow of the Judged Category winners.