Chroococcus minimus is a species of cyanobacteria in the family Chroococcaceae, representing one of the smaller-celled members of the genus, as the specific epithet indicates. Chroococcus is a cosmopolitan cyanobacterial genus found across a wide range of aquatic and moist terrestrial habitats globally. The cells of Chroococcus minimus are spherical, very small in diameter, and occur in pairs or tetrads enclosed within a thin, often inconspicuous mucilaginous sheath. Despite their miniature scale, these organisms are photosynthetically active and contribute to primary production in their aquatic environments. Small-celled cyanobacteria like Chroococcus minimus may dominate the picoplankton fraction of oligotrophic freshwater bodies, where their small cell volume provides a favorable surface area to volume ratio for nutrient uptake in nutrient-limited conditions. Chroococcus minimus has been documented from freshwater habitats in Europe and elsewhere. Identification of small-celled Chroococcus species is challenging due to overlapping morphological characteristics and the influence of environmental conditions on cell dimensions. Molecular phylogenetic studies have substantially revised the taxonomy of coccoid cyanobacteria. The species has not been assessed by the IUCN.