Sign language is a visual language expressed through physical movements instead of spoken words. The language relies on visible cues from hands, eyes, facial expressions, and movements to communicate. Although sign language is used primarily by people who are deaf or hard of hearing, it is also used by many hearing people. As with any spoken language, sign language has grammar and structure rules, and it has evolved over time.

Just like with spoken languages, there is no “universal” sign language. Different countries typically have their own version of sign language, which is unique to their region and culture. For example, American Sign Language (ASL) is different from Australia’s Auslan sign language, which is different from the British Sign Language (BSL) used in the United Kingdom. A person fluent in ASL may travel to Sydney, Australia, and have trouble understanding someone using a local version of sign language—instead of different dialects or accents apparent in oral language, the signs and gestures are different.

Today, there are more than 300 different sign languages in the world, spoken by more than 72 million deaf or hard-of-hearing people worldwide.

In the United States, ASL has become the dominant sign language among the deaf and hard-of-hearing communities. There is no single “inventor” of ASL, but linguists and historians believe it may have evolved from French Sign Language (LSF) more than 200 years ago. Today, ASL is used by more than a million people. More and more, ASL is taught by many schools and colleges as part of modern and “foreign” language classes.

Sign language is a powerful way for people of all hearing abilities to communicate. It can even be used to communicate with gorillas (Gorilla gorilla). In the 1970s, language researcher Dr. Penny Patterson began working with Koko, a western lowland gorilla (Gorilla gorilla gorilla), teaching her sign language. Research has shown that gorillas (and other large apes) have language skills similar to those of small children, and throughout her life, Koko learned more than 1,000 different signs. Koko was able to have entire conversations in sign language, as well as play word games and make up her own signs.