ACH

"Ach" is a common German language interjection that closely resembles English "Oh".

ACH is also a three-letter abbreviation that may refer to:
*Accion contra el Hambre, an International NGO, part of the Action against Hunger (ACF) International Network
* Acetylcholine (ACh), a neurotransmitter
* Acetone cyanohydrin, a highly toxic organic compound.
* ACH Food Companies (AC HUMKO from 1995 to 2000), an American subsidiary of Associated British Foods, previously part of Kraft Foods from 1952 to 1995.
* Achnashellach railway station, in the United Kingdom, from the National Railway code
* Acholi language (ach), as the ISO 639 code for the language
* Achondroplasia, a type of genetic disorder that is a common cause of dwarfism
* AC Horsens, a Danish football club
* Adrenocortical hormone
* Advanced Combat Helmet
* Alberta Children's Hospital, located in Calgary, Alberta, Canada
* Altenrhein Airport, in Switzerland, from its IATA airport code
* American College of Heraldry, an heraldic organization in the United States
* Analysis of Competing Hypotheses
* Angeles Crest Highway
* Arkansas Children's Hospital in Little Rock, Arkansas
* The Association Of Children’s Hospices
* Automated Clearing House, an American electronic banking network often used for direct deposit and electronic bill payment.
* Automotive Components Holdings, LLC, a Ford-managed temporary company mandated to dispose of unprofitable operations of Visteon, its former parts division
* Air Change per Hour, is a unit in ventilation meaning the number of times the air in a room is changed per hour.Ach may refer to the following rivers in Germany and Austria:
*Bregenzer Ach, a tributary of Lake Constance
*Dornbirner Ach, a tributary of Lake Constance
*Friedberger Ach, a tributary of the Lech