According to the World Federation of the Deaf, there are approximately 72 million deaf people worldwide. More than 80% of them live in developing countries. Collectively, they use more than 300 different sign languages.
Sign languages are fully fledged natural languages, structurally distinct from the spoken languages. There is also an international sign language, which is used by deaf people in international meetings and informally when travelling and socializing. It is considered a pidgin form of sign language that is not as complex as natural sign languages and has a limited lexicon. (source: UN)