Posio is a municipality of Finland. It is located in the province of Lapland. The municipality has a population of 2,826 (31 December 2025) and covers an area of 3,544.90 square kilometres (1,368.69 sq mi) of which 506.14 km² (195.42 sq mi) is water. The population density is 0.93 inhabitants per square kilometre (2.4/sq mi). Neighbour municipalities are Rovaniemi, Kemijärvi, Ranua, Salla, Kuusamo, Taivalkoski and Pudasjärvi.

The municipality has a single language, Finnish.

Major employers in Posio are the municipality itself, a major pottery manufacturer Pentik and agriculture (especially dairy farming).

The European route E63 runs through the northern-eastern parts of the municipality.

Korouoma canyon and natural reserve is located in Posio.

8 kilometres (5.0 mi) north of the center of Posio is a microstate called Valtio [fi], founded by Ari "Paska" Peltonen in 2006.

Posio's most renowned attractions are the Pentik-mäki Culture Centre, Riisitunturi National Park, Korouoma Nature Reserve, and the clear waters of lakes Kitkajärvi and Livojärvi. There are also many outdoor recreational things to do in Posio.

The world's northernmost ceramics factory is located in Posio. Pentik Oy interior design company was established in 1971 by Anu and Topi Pentikäinen.