Eukaryotic unicellular organisms such as ciliates (Protist) represent an excellent model system to discover biomineralization principles with respect to intracellular mechanisms involved in ion accumulation, vesicular transport, and biomineral formation. There are over 8,000 species of the Phylum Ciliophora and since ciliates naturally occur in freshwater, brackish, and marine habitats as well as in extreme environments, they can be used to study the effects of different environmental conditions, e.g. available elements. We combine dynamic in vivo studies of mineral-forming ciliates together with high-resolution methods like analytical electron microscopy, to identify common principles and to distinguish diverse mechanisms with specific adaptations involved in mineral formation. Examples include insights into the biomineralization process of CaCO₃ in the ciliate Coleps hirtus, as well as modified mineralization processes in other ciliate species and the characteristics and various functions of the minerals formed. The huge diversity of minerals formed by ciliates offers the possibility to identify interesting biomineralization processes and to transfer this knowledge to other research areas addressing e.g. materials and systems inspired by biomineralization.