Rautjärvi is a municipality in the South Karelia region of Finland. The municipality has a population of 3,032 and covers an area of 401.89 square kilometres of which 50.25 km2 is water. The population density is 8.63 inhabitants per square kilometre. More than half of Rautjärvi's residents live in Simpele, the administrative center of the municipality. The neighboring municipalities of Rautjärvi are Parikkala and Ruokolahti, while to the east is the Russian border.