The alpaca (Lama pacos) is a species of South American camelid mammal. Traditionally, alpacas were kept in herds that grazed on the level heights of the Andes of Southern Peru, Western Bolivia, Ecuador, and Northern Chile. More recently, alpacas may be found on farms and ranches worldwide, with thousands of animals born and raised annually. Alpacas are especially popular in North America, Europe, and Australia.

There are two modern breeds of alpaca, separated based on their respective region of endemism and fiber (wool) type: the Suri alpaca and the Huacaya alpaca. Both breeds produce a highly valued fiber, with Suri alpaca's fiber growing in straight "locks," while Huacaya fiber has a "crimped," wavy texture and grows in bundles. These breeds' fibers are used for making knitted and woven items, similar to sheep's wool.

Alpacas are visually and genetically similar to, and often confused with a relative species, the llamas; however, alpacas are visibly shorter and predominantly bred for their wool, while llamas have long been more highly prized as livestock guardians (in place of dogs), and as a pack animal (beast-of-burden), owing to their nimble mountain-climbing abilities. Nonetheless, all four South American camelids are closely related and can successfully crossbreed. Both the alpaca and the llama are believed to have been domesticated and selectively bred from their wild counterparts — the smaller, fine-haired vicuña and the larger, stronger guanaco, respectively — at least 5,000 to 6,000 years ago.

Alpacas communicate through body language, spitting to show dominance when distressed, fearful, or agitated. Male alpacas are more aggressive than females. In some cases, alpha males will immobilize the head and neck of a weaker or challenging male to show their strength and dominance.

In the textile industry, "alpaca" primarily refers to the hair of Peruvian alpacas. More broadly, it refers to a style of fabric originally made from alpaca hair, such as mohair, Icelandic sheep wool, or even high-quality wool from other breeds of sheep. In trade, distinctions are made between alpacas and the several styles of mohair and luster.

The relationship between alpacas and vicuñas was disputed for many years. In the 18th and 19th centuries, the four South American lamoid species were assigned scientific names. At that time, the alpaca was assumed to be descended from the llama, ignoring similarities in size, fleece, and dentition between the alpaca and the vicuña. Classification was complicated by the fact that all four species of South American camelid can interbreed and produce fertile offspring. The advent of DNA technology made a more accurate classification possible.

In 2001, the alpaca genus classification changed from Lama pacos to Vicugna pacos, following the presentation of a paper on work by Miranda Kadwell et al. on alpaca DNA to the Royal Society showing the alpaca is descended from the vicuña, not the guanaco.

An adult alpaca generally is between 81 and 99 centimetres (32 and 39 inches) in height at the shoulders (withers). They usually weigh between 48 and 90 kilograms (106 and 198 pounds). Raised in the same conditions, the difference in weight can be small with males weighing around 22.3 kilograms (49 lb 3 oz) and females 21.3 kilograms (46 lb 15 oz).