This COST Action is broad in its technical and scientific scope, as its central aim is to bring together people working in quite diverse fields but with a common scientific interest: namely, the understanding and exploitation of the responses of micro-organisms to low pH. These organisms in this context include bacteria, yeasts, and other fungi. This topic is already being studied in considerable depth and has many important practical applications in a number of diverse sectors; however, these sectors traditionally do not communicate well with each other. A new forum for communication will be highly beneficial both for scientific progress and, importantly, for the applied fields in which this topic is important. These include the microbiology of food and drink, many aspects of industrial biotechnology and bio-processing, and clinical and veterinary treatment of infections in a time of increasing antimicrobial resistance. Through a combination of Working Groups, workshops, Short-Term Scientific Missions, and dissemination activities, plus open conferences, this Action will (a) aid increased understanding of the details of how micro-organisms detect and respond to low pH (b) ensure that technical developments being made in one field are rapidly translated into other fields (c) leverage the many different areas of expertise that exist across Action members and (d) ensure, through participation and dissemination, that these developments reach as wide an audience as possible, including pure and applied scientists in the Inclusiveness Target Countries.