Proto-Sámi is the hypothetical, reconstructed common ancestor of the Sámi languages. Its reconstructed ancestor is the Proto-Uralic language.

Proto-Sámi descends from Proto-Uralic. Finnic languages and Sámi languages are currently geographically adjacent and coexisting in the same areas. However, whether or not they are linguistically closely related is disputed. That is, the validity of a separate grouping of "Finno-Sámic languages" not universally accepted and the existence of a separate "Proto-Finno-Sámic language" as parent language of Proto-Sámic is uncertain. Valter Lang (of University of Tartu) posits that the Baltic Finns and the Sámi were already separate linguistic groups before they left the Uralic core area, and arrived to Fennoscandia via different routes. The Sámi entered Fennoscandia from the east or southeast. In contrast, Baltic Finns took a southern route from the Daugava river (in today's Latvia) to northern Estonia and over the sea into western Finland. This makes a separately developed Finno-Sámic language chronologically untenable. Instead, if the Finno-Sámic group existed, it was at best a group of western Proto-Uralic dialects, not a separately language.

Although the current Sámi languages are spoken much further to the north and west, Proto-Sámi was likely spoken in the area of modern-day Southwestern Finland around the first few centuries CE. Local (in Sápmi) ancestors of the modern Sámi people likely still spoke non-Uralic, "Paleoeuropean" languages at this point (see Pre-Finno-Ugric substrate). This situation can be traced in placenames as well as through the analysis of loanwords from Germanic, Baltic, and Finnic. Evidence also can be found for the existence of language varieties closely related to but likely distinct from Sámi proper having been spoken further east, with a limit around Lake Beloye.

There is abundant toponymic evidence of Sámi settlement in even the southern parts of Finland, and the Sámi coexisted with Finns and Swedes in southern Finland as late as the 14th century. Separation of the main branches (West Sámi and East Sámi) is also likely to have occurred in southern Finland, with these later independently spreading north into Sápmi. The exact routes of this are not clear: it is possible Western Sámi entered Scandinavia across Kvarken rather than via land. Concurrently, Finnic languages that would eventually end up becoming modern-day Finnish and Karelian were being adopted in the southern end of the Proto-Sámi area, likely in connection with the introduction of agriculture, a process that continued until the 19th century, leading to the extirpation of original Sámi languages in Karelia and all but northernmost Finland.

The Proto-Sámi consonant inventory is mostly faithfully retained from Proto-Uralic, and is considerably smaller than what is typically found in modern Sámi languages. There were 16 contrastive consonants, most of which could however occur both short and geminate:

Stop and affricate consonants were split in three main allophones with respect to phonation:

The spirant *δ also had two allophones, voiceless [θ] occurring word-initially and syllable-finally, and voiced [ð] elsewhere.

A detailed system of allophony is reconstructible, known as consonant gradation. Gradation applied to all intervocalic single consonants as well as all consonant clusters. This is unlike gradation in the related Proto-Finnic and its descendants, where it applied only to a subset. The conditioning factor was the same, however: the weak grade occurred if the following syllable was closed, the strong grade if it was open. This difference was originally probably realized as length: