American Sign Language, also known as ASL or Ameslan (old term), is a language in visual-spatial modality. It is dominantly used by culturally Deaf people in the U.S. and speaking-English Canada. ASL is the 3rd or 4th most used language in the U.S.
The minister Thomas Hopkins Gallaudet met a little deaf girl, Alice Cogswell, in his neighborhood in Connecticut. Dr Cogswell and Gallaudet were interested in deaf education. There were no deaf schools in the U.S. at that time. Gallaudet traveled to England and then France to learn about deaf education and teaching methods.
Gallaudet was invited to visit the public school for the deaf in Paris. There Gallaudet asked a brilliant young deaf teacher, Laurent Clerc to come to America with him. They founded the first permanent school for the deaf, American Asylum (now the American School for the Deaf) in Hartford, Connecticut in 1817.
The Old French Sign Language (OFSL) that Clerc brought to the U.S. was intermingled with the previous native sign languages. ASL has been evolved since then.
In the 1960s, William Stokoe, a hearing English professor at Gallaudet University (formerly Gallaudet College), observed sign language used by the Gallaudet students. He studied and discovered that it had linguistic features (phonology, morphology, syntax, and all) like any spoken language. He researched and proclaimed that it is a language. His works were published in linguistics journals. Since the 1970s, a number of research and studies have quickly grown.
Today millions of Deaf people speak ASL on a daily basis. There are many ASL courses provided in secondary and post-secondary schools, continuing education programs, and private classes in the U.S. today.