<p>Acid-sulphate soils (ASS) are worldwide naturally or anthropogenically formed soils that originate from the oxidation of pyrite in anoxic sulfide substrates. Classification of soils into ASS types is complex and usually depends on grain size, oxidation rates, pH values, acidification potential and typical microbial communities. Currently, there is not a consensual classification of ASS and definitions are not universally applied. The global use of ASS for crops and mining areas has become an environmental problem, raising concerns in the scientific community and prompting the study of microorganisms inhabiting this acidic environment and their potential for further use in bioremediation processes. Globally, ASS harbor a higher abundance of the bacterial phylum Pseudomonadota, especially members of the Beta and Gammaproteobacteria classes, followed by other less abundant phyla like Bacillota, Actinomycetota, Acidobacteriota, Bacteroidetes, Nitrospirota and Chloroflexota. Among the archaea reported in ASS are members of the genera <i>Thermoproteus</i> and <i>Acidilobus</i> and of the Thermoplasmata class. Bacteria and archaea found in the different types of ASS exhibit diverse metabolisms, including dissimilatory processes like iron and/or inorganic sulfur oxidation, iron or sulfate reduction, aluminum and iron reduction and methanogenesis, assimilatory processes like autotrophy, diazotrophy, and other metabolic properties such as phosphate solubilization and acidogenesis. This diversity offers a wide range of biotechnological applications, including bioremediation of crop areas and natural ecosystems affected by acidity and a vast field for basic and applied scientific research.</p> Graphical Abstract <p></p>