From a biomineralization point of view, the protist world is far less investigated than its metazoan counterpart. However, eukaryotic single-celled organisms offer a very unique access to discover biomineralization mechanisms in vivo. With respect to intracellular mechanisms involved in ion enrichment, mineral transport or vesicle formation ciliates represent a good model system. One important group of protists, the ciliates, is very common and numerous studies have been performed on their ecology, cell biology, morphology or genetics. Ciliates are also known for their formation of diverse mineralized intracellular and extracellular structures. However, only limited numbers of detailed studies on the kind of minerals, their properties or their formation mechanisms have been reported so far. This article reviews older and more recent literature on biomineralization in ciliates.