Cowlitz (Cowlitz: ), also known as Cowlitz Salish, is a Tsamosan language of the Coast Salish family of Salishan languages. It was spoken by the Lower Cowlitz people of the Cowlitz Indian Tribe and is spoken today by both Lower and Upper Cowlitz people. It went dormant in the 1960s. As of 2022, it is being revitalized by the Cowlitz Tribe in collaboration with the Language Conservancy.
Cowlitz had two dialects, with a dialectal opposition between and and and . However, these dialects were poorly documented, due to the extinction of the language.
The Cowlitz people were originally two distinct tribes: the Lower Cowlitz and the Upper Cowlitz, sometimes called the Taidnapam. Only the Lower Cowlitz originally spoke Cowlitz Salish. The Upper Cowlitz spoke a Sahaptin language.
Cowlitz is most similar to Lower Chehalis, another Tsamosan language, although it contains some oddities, such as the word for one, utsus (in contrast to the Lower Chehalis paw).