Petco sells pet food, products, and services, as well as certain types of live small animals.

Some stores offer services such as obedience training, dog grooming, pet vaccinations, and veterinary care, while also hosting adoption events.

Petco originated when Walter Evans, a co-owner of a Missouri-based distributor of pet supplies and products[8] called United Pharmacal Company (UPCO), moved to San Diego County, California.

In San Diego County in 1965, Evans initially set up a mail-order veterinary supply business with five associates.

[9] Evans opened his first retail store in 1976 in La Mesa, California, selling pet and veterinary supplies.

[14] To compete with supermarkets, Petco focused on premium pet-food brands such as IAMS, Science Diet, and Nutro, which were introduced in the mid-1980s.

[15] In 1988 Petco acquired two other West Coast chains, Wellpet, Inc. and The Pet Department,[8] bringing its store number to 130.

[8] By 1990 Petco was heavily in debt, and Brian K. Devine of Toys "R" Us was hired to turn the company around as president and CEO.

Devine rebranded the acquired WellPet and Pet Department stores Petco, also hiring new leadership and extending the chain's credit.

Devine eschewed a big-box discount store model, instead prioritizing premium merchandise such as natural or organic pet food.

[17] Petco introduced Red Ruff the dog and Blue Mews the cat as its logo mascots in 1991, and the following year it adopted the tagline "Where the pets go".

[23][24] In 1997 Petco acquired 104 new stores,[25] in large part from purchasing the competing chain PetCare in the Midwest and South.

[26] The aggressive growth in 1997 proved costly,[27] and in 1998 Petco accrued $8 million in net losses and its stock value dropped significantly.

[33] With LGP and TPG contributing $92.5 million each in equity,[34] their buyout deal closed in October 2000 and Petco was taken off the NASDAQ.

[42] In the wake of reported distribution accounting errors,[43] Petco's stock in mid July 2006 had dropped 50% from a high in January 2005.

Foster and Smith subsidiary in early 2019, redirecting the e-commerce site to Petco.com[54] and filling prescriptions via Express Scripts.

The IPO raised $864 million, and CVC Capital Partners and Canada Pension Plan Investment Board retained control as majority owners.

[86] The Unleashed stores mainly sell natural dog and cat foods and do not carry live animals.

The smaller Unleashed stores are intended to create a community feeling, hosting pet parties and offering services such as adoption events,[87] dog training, and vaccinations.

[89] In September 2011, a Petco location in Johnson City, New York came under fire when nearly 100 animals drowned during a flood caused by Tropical Storm Lee.

[90] Despite severe weather warnings and flood advisories for the nearby river in the days prior, including from the National Weather Service (as stated by the Johnson City police), Petco initially claimed it had not received warnings, and that the casualties were caused by a backup in the store's drain/sewage line, not by the flooding that submerged the store in four feet of water.

Johnson City Mayor Dennis Hannon called Petco's initial claims "absurd", and stated that "for them not to go down there is just absolutely disgusting", alluding to the sewer/drain line backup being only a small part of the problem.

[90][91][92] On September 12, 2011, Petco issued a statement accepting full responsibility for the event, saying that they "misjudged" the risk of a flood.

[101] In 2021, Petco debuted its "Love Lost facial recognition program", which uses a database to help locate missing dogs in the shelter system.