Animal languages are forms of communication between animals that show similarities to human language. Animals communicate through a variety of signs, such as sounds and movements. Signing among animals may be considered a form of language if the inventory of signs is large enough, the signs are relatively arbitrary, and the animals seem to produce them with a degree of volition (as opposed to relatively automatic conditioned behaviors or unconditioned instincts, usually including facial expressions).

Many researchers argue that animal communication lacks a key aspect of human language, the creation of new patterns of signs under varied circumstances. Humans, by contrast, routinely produce entirely new combinations of words. Some researchers, including the linguist Charles Hockett, argue that human language and animal communication differ so much that the underlying principles are unrelated. Accordingly, linguist Thomas A. Sebeok has proposed to not use the term "language" for animal sign systems. However, other linguists and biologists, including Marc Hauser, Noam Chomsky, and W. Tecumseh Fitch, assert that an evolutionary continuum exists between the communication methods of animal and human language.

Some experts argue the following properties separate human language from animal communication:

Research with apes, like that of Francine Patterson with Koko (gorilla) or Allen and Beatrix Gardner with Washoe (chimpanzee), suggested that apes are capable of using language that meets some of these requirements, including arbitrariness, discreteness, and productivity.

In the wild, chimpanzees have been seen "talking" to each other when warning about approaching danger. For example, if one chimpanzee sees a snake, said chimpanzee may make a low, rumbling noise, signaling for all the other chimps to climb into nearby trees. In this case, the chimpanzees' communication does not indicate displacement, as it is entirely contained to an observable event.

Arbitrariness has been noted in meerkat calls; bee dances demonstrate elements of spatial displacement; and cultural transmission has possibly occurred through language between the bonobos named Kanzi and Panbanisha.

Claims that animals have language skills akin to humans, however, are extremely controversial. In his book The Language Instinct, Steven Pinker illustrates that claims of chimpanzees acquiring language are exaggerated and rest on very limited or specious evidence.

The American linguist Charles Hockett theorized that there are sixteen features of human language that distinguish human communication from that of animals. He called these the design features of language. The features mentioned below have so far been found in all spoken human languages, and at least one is missing from any other animal communication system.