Abandoned pets are companion animals that are either inadvertently or deliberately cast off by their owners. These animals can be left alone on the property or streets, be re-homed to a friend or family member, or relinquished at an animal shelter.
Approximately 6.5 million companion animals enter U.S. animal shelters nationwide every year.  Pets are abandoned for a variety of reasons, including family disruption (divorce, death), foreclosure, economic problems, or minor behavioral issues. The overwhelming barrier for many pet owners is financial, with 80% being unable to obtain preventative care for their pets due to financial constraints, 74% for sick care, and 56% for emergency care. Lack of access to veterinary care is a threat to the wellbeing of pets and can lead to the relinquishing of pets and ultimately euthanasia. 
Studies show that the majority of people who relinquish an animal also report being emotionally attached to the dog. It has been reported that when forced to abandon their animals in an evacuation, people suffer mental issues such as grief, depression, and post-traumatic stress disorder. Recognizing the importance of pets to their owners and their role in public health is an essential first step in improving a public health problem that has been seen repeatedly in the past and is unlikely to change in the future.
Often, when abandoned, pets are forced to fend for themselves and become stray or feral. In particular, cats and dogs go to colonies. Feral cats are said to outnumber feral dogs and can become challenging to handle and socialize enough to be re-introduced to a new human owner. In general, only some newly abandoned cats and very young feral kittens can be tamed.
Stray animals increase potential exposure to zoonotic diseases like rabies. Cat bites or scratches involving stray or feral animals are eight times more common than dog bites.
Currently, the exact number of foreclosed pets is unknown. People often drop animals off at a shelter and claim they are moving, when in fact, they are leaving due to foreclosure. In 2008, the number of foreclosure pets was believed to had increased due to high foreclosure rates. As homeowners run out of time and options, they often leave their animals behind. The animals are then classified as abandoned foreclosure pets.
The pets left behind in homes are often left without food or water. Some do not survive because of the lack of resources and are found dead when realtors or banks enter the premises. The animals are put in harm's way, and it is often believed it is done as a way to retaliate against those who took the home away.
Many animals left at a shelter are euthanized due to a lack of space and financial resources for these animals. Shelters unable to raise additional funds to provide for the increased number of incoming animals have no choice but to euthanize them, sometimes within days. 
However, the number of dogs and cats euthanized in U.S. shelters declined from approximately 2.6 million in 2011 to 1.5 million in 2018. This decline can be partially explained by an increase in the percentage of animals adopted, and an increase in the number of stray animals successfully returned to their owners. 
In many states in the United States, it is a felony to abandon a pet. In New York, it is considered a misdemeanor, and the recent senate bill S410 proposes to increase the maximum fine for the crime of abandonment of animals to $2,000. 
However, there is still a necessity to investigate interventions to prevent companion-animal relinquishment. 
For Pet owners having trouble affording their pets, many national organizations can help. The humane Society completed them here.