Achern (German: [ˈaxɐn] ⓘ; Low Alemannic: Achre) is a city in Western Baden-Württemberg, Germany.

Achern is the fourth largest town in the district of Ortenau (Ortenaukreis), after Offenburg, Lahr / Black Forest and Kehl.

As subsequent to the district reform in the 1970s the population passed the 20,000 mark, Achern requested to be awarded the status of Große Kreisstadt.

Besides Achern itself, the municipality includes the boroughs of Fautenbach, Gamshurst, Großweier, Mösbach, Oberachern, Önsbach, Sasbachried and Wagshurst.

The Acher then continues on in northwesterly direction between Fautenbach and Großweier and south of Gamshurst, before leaving the city to head for the Rhine.

The largest lake is called Achernsee, near the Achern Autobahn ramp, in the West of the city.

Achern is surrounded by the following communities (starting clockwise from the north): Lichtenau and Ottersweier (both Rastatt District), as well as Sasbach (Ortenau), Lauf (Baden), Sasbachwalden, Kappelrodeck, Renchen, and Rheinau (Baden), all part of Ortenau District.

Within the municipal borders of Achern, the city is made up of the city center (Kernstadt), and the boroughs that were redistricted into Achern during the District Reform in the 1970s, namely, Fautenbach, Gamshurst, Großweier, Mösbach, Oberachern, Önsbach, Sasbachried and Wagshurst.

Examples of such neighborhoods are Litzloch, Michelbuch and Ziegelhütte in Gamshurst, Malghurst in Sasbachried, Lindenhof in Fautenbach and Schollenhof in Wagshurst.

During the High Middle Ages the town became part of the German Reich, courtesy of the Staufenberger and Zähringer families, and was included in the Landsvogtei of Ortenau.

The Protestant parish also serves the boroughs of Oberachern, Fautenbach, Gamshurst, Großweier and Sasbachried as well as the neighboring towns of Sasbach, Obersasbach and Lauf.

Also represented in Achern, though in smaller numbers, are Muslims, Jehovah's Witnesses, New Apostolic Church, and Seventh-day Adventists.

Since becoming part of Baden, the Mayor and City Council attend to Achern's local administration.

As Achern is the center of the otherwise rural region of northern Ortenau District, small merchant enterprises are very important.

In Achern, the Badischen Neuesten Nachrichten (BNN), a daily newspaper operating out of Karlsruhe, publishes a local edition by the name of Acher und Bühler Bote and the Offenburger Tageblatt publishes its local edition as Acher-Rench-Zeitung.

Achern is the seat of a district court, the Finance Ministry maintains an office, and residents can find a notary public.

Achern has a college-track highschool (Gymnasium Achern), a non-college-track highschool (Robert-Schumann-Realschule), a school for the learning disabled (Achertalschule), three grammar and middle schools with a vocational highschool (Antoniusschule Oberachern, Grund- und Hauptschule mit Werkrealschule Achern, Grund- und Hauptschule Önsbach and Vinzenz-Wachter-Schule), as well as five grammar schools, one each in the boroughs of Gamshurst, Grossweier, Mösbach, Sasbachried and Wagshurst.