Blackfoot, also called Niitsíʼpowahsin (ᖹᒧᐧᑲᖷᐦᓱᐡ) or Siksiká (/ˈsɪksəkə/ SIK-sə-kə; Blackfoot: [sɪksiká], ᓱᖽᐧᖿ), is an Algonquian language spoken by the Blackfoot or Niitsitapi people, who currently live in the northwestern plains of North America. There are four dialects, three of which are spoken in Alberta, Canada, and one of which is spoken in the United States: Siksiká / ᓱᖽᐧᖿ (Blackfoot), to the southeast of Calgary, Alberta; Kainai / ᖿᐟᖻ (Blood, Many Chiefs), spoken in Alberta between Cardston and Lethbridge; Aapátohsipikani / ᖳᑫᒪᐦᓱᑯᖿᖹ (Northern Piegan), to the west of Fort MacLeod which is Brocket (Piikani) and Aamsskáápipikani / ᖳᐢᐧᖿᑯᑯᖿᖹ (Southern Piegan), in northwestern Montana. The name Blackfoot probably comes from the blackened soles of the leather shoes that the people wore.

There is a distinct difference between Old Blackfoot (also called High Blackfoot), the dialect spoken by many older speakers, and New Blackfoot (also called Modern Blackfoot), the dialect spoken by younger speakers. Among the Algonquian languages, Blackfoot is relatively divergent in phonology and lexicon. The language has a fairly small phoneme inventory, consisting of 11 basic consonants and three basic vowels that have contrastive length counterparts. Blackfoot is a pitch accent language. Blackfoot language has been declining in the number of native speakers and is classified as either a threatened or endangered language, depending on the source used.

Like the other Algonquian languages, Blackfoot is considered to be a polysynthetic language due to its large morpheme inventory and word internal complexity. A majority of Blackfoot morphemes have a one–to–one correspondence between form and meaning, a defining feature of agglutinative languages. However, Blackfoot does display some fusional characteristics as there are morphemes that are polysemous. Both noun and verb stems cannot be used bare but must be inflected. Due to its morphological complexity, Blackfoot has a flexible word order.

The Blackfoot language has experienced a substantial decrease in speakers since the 1960s and is classified as "definitely endangered" by the UNESCO Atlas of the World's Languages in Danger. In Canada, this loss has been attributed largely to residential schools, where Indigenous students were often punished severely for speaking their first languages. Widespread language loss can also be attributed to the Sixties Scoop, through which thousands of Indigenous children were taken from their families, often without parental consent, and relocated by the government into non-Indigenous families. As a result of these losses, the Blackfoot community has launched numerous language revitalization efforts, include the Piikani Traditional Knowledge Services and many more.

The four main Blackfoot dialects are Siksiká (ᓱᖽᐧᖿ), Káínai (ᖿᐟᖻ), Aapátohsipikani (ᖳᑫᒪᐦᓱᑯᖿᖹ), and Aamsskáápipikani (ᖳᐢᐧᖿᑯᑯᖿᖹ). Some words are different in each dialect, for example: potato, in the Kainai dialect is maatááki but in Piikani dialect is paatááki, and another example: coffee, in Blackfoot dialects in Canada, is niitáʼpaisiksikimi but in the Aamsskáápipikani dialect is áísiksikimi.

There is also minor grammatical and phonological differentiation between dialects.

During language revitalization courses educators frequently had situations where the Blackfoot the students learnt from their older relatives was different from the modern Blackfoot they were being taught. The modern variety's words are usually contracted compared to the older varieties.

Some words are written in their uncontracted forms while in everyday spoken speech they are instead presented in their contracted forms, these spoken aside from being contracted are also less morphologically compositional than their written forms.