Nepalese Sign Language or Nepali Sign Language (Nepali: नेपाली साङ्केतिक भाषा, romanized: Nēpālī Sāṅkētika Bhāṣā) is the main sign language of Nepal. It is a partially standardized language based informally on the variety used in Kathmandu, with some input from varieties from Pokhara and elsewhere. As an indigenous sign language, it is not related to oral Nepali. The Nepali Constitution of 2015 specifically mentions the right to have education in Sign Language for the deaf. Likewise, the newly passed Disability Rights Act of 2072 BS (2017 CE) defined language to include "spoken and sign languages and other forms of speechless language." in practice it is recognized by the Ministry of Education and the Ministry of Women, Children and Social Welfare, and is used (albeit in a somewhat pidginized form) in all schools for the deaf. In addition, there is legislation underway in Nepal which, in line with the UN Convention on the Rights of Persons with Disabilities (UNCRPD) which Nepal has ratified, should give Nepalese Sign Language equal status with the oral languages of the country.

Nepalese Sign Language may have originated in the first school for the deaf in Nepal, established in Kathmandu in 1966 by an ENT doctor. The school was later moved to a children's home in Naxal. The aim of the school was to teach speech therapy to deaf children to have them learn to speak. Even so, deaf people who went to the school at this time recall using signs with each other during and after school. The oral policy continued until the arrival of the Patricia Ross, who tried to have total communication introduced into the school in 1985.

In 1980, 13 deaf Kathmandu youths established the Deaf Welfare Association, which would later become the Kathmandu Association of the Deaf (KAD). This was the first association of any type established by disabled themselves and run under their own leadership and management. One of the chief goals of KAD was social reform of deaf people with an effort to promote and further develop sign language. At the time sign language was still banned in the deaf school; however, KAD worked hard to keep it alive at Deaf gatherings on weekends. Later KAD developed a one-handed fingerspelling system for Devanagari with the support of UNICEF.

The first NSL dictionary was undertaken by American Patricia Ross in conjunction with KAD. Because of this connection, there may have been influence from ASL during the process.

Generally speaking then, NSL developed as a natural language established by the Deaf community of Kathmandu valley, but it has been influenced by other sign languages, as well as artificial systems of sign such as Total Communication or Simultaneous Communication. This influence from outside due to contact (with, for example Indo-Pakistani Sign Language and with structural principles introduced from artificial sign systems used in the United States) was strong during its initial stage of the formation, but in different ways and to different degrees remains strong to this day (although the contact is more with International Sign, American Sign Language and various European sign languages used by visiting deaf tourists and by deaf from European funding organizations). There are also semantic overlaps with spoken Nepali (and perhaps other spoken languages).

Nepalese Sign Language is not used natively by the overwhelming majority of deaf people in Nepal. Since the overwhelming majority of deaf children in Nepal, as in all countries, are born into hearing families without a single signing member, Nepalese Sign Language is primarily learned first at schools for the deaf. However, these schools are few in number, and not readily accessible to most, and so most deaf Nepalese have no opportunity to acquire Nepalese Sign Language under normal circumstances.

While the vast majority of non-hearing Nepalese do not have the opportunity to acquire NSL, those who are a part of the country's active Deaf communities are often well-connected to a wide international network of signers through formal relationships with foreign Deaf organizations and personal relationships with foreign signers.

Researchers have discussed the homesign systems generated by Deaf Nepalese in the absence of or in addition to NSL, which are one source of linguistic variation in the language, and the potential impact of late exposure to NSL on signing practice. Scholars have also noted that first exposure to signing practice often takes place in schools for the deaf, where classes are taught primarily by hearing teachers who use Signed Nepali, which can become another source of variation in Deaf Nepalese's signing repertoire.