It is widely recognized in the fields of linguistics and anthropology that one of the most important issues facing humankind today is the rate at which our languages are dying. If the present trend continues, during the 21st century more than half of the world's 7000 languages could become extinct, and most of these will vanish without being adequately recorded. The Linguistic Society of America (LSA) and the National Science Foundation (NSF) have recognized the extreme urgency of documenting and describing endangered languages. With 2009 – 2011 support from the NSF's Linguistics Division (BCS-0853665 and BCS-1027735), Documenting Endangered Languages (DEL) Program, this project aims to: describe the linguistic nature and underpinnings of PISL; bring together sign language linguists and members of the PISL signing community for the purpose of language documentation, description, and to draw attention to this important, yet often times overlooked part of American Indian cultural and linguistic heritage. The project also provided PISL Linguistic Documentation Workshops on the Northern Cheyenne reservation, August 11 – 15, 2010, in collaboration with stakeholders from American Indian communities and tribal colleges.