Body language is a type of communication in which physical behaviors, as opposed to words, are used to express or convey information. Such behavior includes facial expressions, body posture, gestures, eye movement, touch and the use of space. The term body language is usually applied in regard to people but may also be applied to animals. The study of body language is also known as kinesics.

Although body language is an important part of communication, most of it happens without conscious awareness.

Body "language" must not be confused with sign language. Sign languages are literally languages: they have (their own) complex grammar systems, and they also are able to exhibit the fundamental properties that are considered to exist in all (true) languages. Body language, on the other hand, does not have a grammar system and must be interpreted broadly, instead of having an absolute meaning corresponding with a certain movement, so it is not a language, and is simply termed as a "language" due to popular culture.

In a society, there are agreed-upon interpretations of particular behavior. Interpretations may vary from country to country, or culture to culture. (On this note, there also is controversy on whether body language is universal.) Body language, a subset of nonverbal communication, complements verbal communication in social interaction. In fact, some researchers conclude that nonverbal communication accounts for the majority of information transmitted during interpersonal interactions. It helps to establish the relationship between two people and regulates interaction, yet it can be ambiguous.