Unicellular algae and diatoms (Bacillariophyta) in particular, have attracted increasing attention as the objects of biotechnology. Diatoms are known to produce mucopolysaccharides, fats, and fat like sub stances suitable for production of biodiesel, unusual pigments (e. g., marennine), and nanosized siliceous structures. It should be noted that only few diatom species out of great number living on the Earth are used in biotechnology. About 100000 species of diatoms occur in nature. The use of diatoms in biotechnology is restricted by little studied life cycle and biology of reproduction. This review summarizes data on biological properties of diatoms, which should be taken into account when they are used as the objects of culturing and particularly as clones.