American Sign Language (ASL) is a complete, complex language that employs signs made with the hands and other movements, including facial expressions and postures of the body. ASL is a language completely separate from English. It contains all the fundamental features a language needs to function on its own. It has its own rules for grammar, punctuation, and sentence order.
Source: National Institute on Deafness and Other Communication Disorders (http://www.nidcd.nih.gov/health/hearing/asl.aspx)