A contact sign language, or contact sign, is a variety or style of language that arises from contact between deaf individuals using a sign language and hearing individuals using an oral language (or the written or manually coded form of the oral language). Contact languages also arise between different sign languages, although the term pidgin rather than contact sign is used to describe such phenomena.

Contact sign has been characterized as "a sign language that has elements of both [a] natural sign language and the surrounding [oral] language".

Language contact is extremely common in most Deaf communities, which are almost always located within a dominant oral language ('hearing') culture. Deaf people are exposed to the oral language that surrounds them, if only in visual forms like lip reading or writing, from early childhood. Within everyday life it is not uncommon for Deaf people to be in contact with oral languages. Hearing parents and teachers of deaf children, if they sign at all, are usually second language learners, and their signing style will exhibit features of interference from the oral language. A mixing of languages and modes may also occur when interpreting between a spoken and a sign language.

While deaf sign languages are distinct from spoken languages, with a different vocabulary and grammar, a boundary between the two is often hard to draw. A language 'continuum' is often described between signing with a strong sign-language grammar to signing with a strong spoken-language grammar, the middle-regions of which are often described as contact sign (or Pidgin Sign). In a conversation between a native signer and a second-language learner, both conversation partners may be signing at different ends of the spectrum. A blend that is often seen is vocabulary from the sign language signed in the word order of the oral language, with a simplified or reduced grammar typical of contact languages. We can recognize that the speaking habits of an English speaker learning French for the first time will differ from those of a native French speaker. The same thing happens when a hearing individual is learning a sign language.

However, even a dialogue between two native deaf signers often shows some evidence of language contact. Deaf people in the United States may use a more English-like signing style in a more formal setting, or if unfamiliar with the interlocutor.

Huenerfauth claims that Pidgin Signed English, as well as contact languages, can create accessibility benefits for users of sign language who have lower levels of written literacy. While Cecil Lucas explains how contact also occurs when deaf signers modify their language for the sake of hearing people who are in the process of learning to use a sign language.

Sign language researchers Ceil Lucas and Clayton Valli have noted several differences between the language contact arising between two sign languages and the contact phenomena that arise between a signed and an oral language.

When two sign languages meet, the expected contact phenomena occurs: lexical borrowing, foreign "accent", interference, code switching, pidgins, creoles and mixed systems. However, between a sign language and an oral language, lexical borrowing and code switching also occur, but the interface between the oral and signed modes produces unique phenomena: fingerspelling (see below), fingerspelling/sign combination, initialisation, CODA talk (see below), TTY conversation, mouthing, and contact signing.