While a raw material may be fairly easily substituted, the use of an organism different from one already in existence may involve extensive experimentation and modification of established processes if the usual products are to be obtained. Therefore, the gene pool of organisms with desirable properties must be preserved and be constantly available. Within the gene pool, there are groups of genes which define strains within the species. In industrial microbiology, the strain is often more valuable than the species as the ability to produce the unique characteristics of a product resides in the strain. Industrial microbiological establishments usually keep a stock of microorganisms (culture collection) which possess the gene pools for producing desired products. Industrially important microorganisms are often mutants, and are preserved under conditions of low metabolic state which limits their tendency to revert to their low-yielding ancestors Accordingly, this chapter explains the importance of culture collections in industrial microbiology and biotechnology, types of culture collections, handling culture collections, methods of preserving microorganisms, microbial preservation methods based on the reduction of the growth temperature, microbial preservation methods based on dehydration, microbial preservation methods based on the reduction of nutrients and determination of the most appropriate method of preserving an organism.