The CALU Culture Collection of microscopic algae and other microorganisms has celebrated its 45^th year of continuous operation in 2003. Although it was originally designed to supply live material for aims of biotechnology in the former USSR, it gradually focused itself on isolation, preservation, classification, and polyphasic research with microscopic algae and their microbial partners. Today CALU is among the largest (794 culturable strains) specialized public service collections; it represents all central aspects of biodiversity except for the archaea - viruses, bacteria, algae, protists, and fungi. Some parasites of algae are uniquely deposited in this collection. The basis of CALU is freshwater eukaryotic algae (400 strains from 49 genera) and cyanobacteria (287 strains from 29 genera) - a replica of the Eurasian domain of these microorganisms. The rest is non-photosynthetic bacteria (61 strains from 4 genera), aphelid protists (12 strains from 2 genera), fungi (19 strains from 5 genera), bacteriophages, and viruses of eukaryotes (15 strains from 2 groups). Live material is maintained as axenic, bacteria-free, and unialgal cultures either in liquid media or on agar slants. Except for thermophiles, microbial strains are stored at 12°C, continuously or periodically illuminated with ca. 7 μE m^-2 s^-1 of cool white light, and reinoculated in 2-3 months. Native research with selected strains of CALU deals with cytology, genetics, molecular biology, biochemistry, physiology, ecology, and taxonomy. All cultures are accessible for free distribution by the official transportation routes.