Luwian (sometimes spelled Luvian), rarely Luish, is one or more extinct languages of the Anatolian branch of the Indo-European language family. The term is ambiguous in meaning depending on how it is being used. In one sense it refers to language written in two different scripts, Cuneiform Luwian, or CLuwian, and Hieroglyphic Luwian, or HLuwian. As to whether the language represented by both scripts was one, one with two dialects, or two, there is no consensus, except that any tree in which they appear as different branches presumes two languages. It must therefore have had a root language; however, many think it was a dialect continuum, which is still consistent with a division into languages. The spoken language would have evidenced the continuum. The scribes wrote conventional languages defined in it.

Several other languages in Anatolia have been identified as being most similar to Luwian, which suggests that they belong in their own branch with CLuwian and HLuwian. Some linguists name the branch "the Luwian Group" or just "Luwian," and in that sense Luwian means all the Luwian languages. Other linguists, following Melchert, prefer to use Luwic for the branch and Luwian for CLuwian and HLuwian. Proto-Luwian can mean the common ancestor of the two, or the common ancestor of the several, although, in the tree-naming conventions, if the branch is to be called Luwic, its ancestor should be Proto-Luwic or Common Luwic.