is a village located in Nagano Prefecture, Japan. , the village had an estimated population of 6,379 in 2360 households, and a population density of 30.7 persons per km<sup>2</sup>. The total area of the village is .
Achi is located in mountainous far southwestern Nagano Prefecture, bordered by Gifu Prefecture to the west. Mount Ena (2191 meters) is on the border of the village with Gifu Prefecture.
The town has a climate characterized by hot and humid summers, and cold winters (Köppen climate classification Dfb). The average annual temperature in Achi is . The average annual rainfall is with July as the wettest month. The temperatures are highest on average in August, at around , and lowest in January, at around .
Per Japanese census data, the population of Achi has decreased over the past 70 years.
The area of present-day Achi was part of ancient Shinano Province. The modern villages of Ochi, Chiri and Goka were established on April 1, 1889, by the establishment of the municipalities system. The three villages merged on September 30, 1956, to form the village of Achi. The neighboring village of Namiai was annexed on January 1, 2006.
On March 31, 2009, the village of Seinaiji, also in Shimoina District, was merged into Achi.
The economy of Achi is based on agriculture, with Jerusalem artichoke, garlic and Yacón as noted local specialities
Achi has five public elementary schools and one public middle school operated by the village government and one private elementary school. The village has one public high school, which is operated by the Nagano Prefectural Board of Education.