The central aim of this COST Action, chaired by Prof. Daniela De Biase, 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. Our activities are organised in 6 Working Groups (WG). The Action is actively training a new generation of scientists by running Training Schools, awarding grants for Short Term Scientific Missions and Conferences, organizing Open Meeting and sharing knowledge with a worldwide community of researchers through webinars organised on a monthly basis (Acidic Friday) and publications. The community has 200+ members and 33 COST Member states participating in it.