Millions of pets are abandoned worldwide every year, which is an important animal welfare and financial problem. This paper was divided into three studies. Our first two studies were designed as a national survey of animal shelters to profile the population of stray dogs and cats, as well as to gather information on both relinquishment and adoption. The aim of our third study was to test the impact of identification on the recovery of dogs entering animal shelters. Studies one and two indicate that more than 100,000 dogs and more than 30,000 cats enter animal shelters annually in Spain. We observed a seasonal effect in the number of admissions in cats. Two-thirds of dogs and cats entering shelters were found as strays, while the rest were relinquished directly to the shelter. Most pets admitted to animal shelters were adult, non-purebred, and without a microchip, with the majority of dogs being medium sized. Adult dogs spent significantly more time in shelters than puppies. While most animals were either adopted or recovered by their owner, a considerable percentage remained at the shelter or was euthanized. The identification of dogs with a microchip increased by 3-fold the likelihood of them being returned to the owner.