Eukaryotic microalgae and prokaryotic cyanobacteria (blue-green algae) have traditionally been maintained by serial subculture, with the frequency of transfer being largely determined by the growth characteristics of the strain. This technique has the dual disadvantages of being labor intensive and carrying risk of loss in genetic stability of the strain. Compared with other groups of microorganisms, relatively little research has been carried out on the development of long-term preservation methods for microalgae and cyanobacteria. Freeze-drying has not been found to be a successful biostorage method for microalgae, with very low levels of viability (<1% of original population) (1, 2) and a further reduction in viability on prolonged storage (3, 4). The successful lyophilization of the cyanobacterium Nostoc muscorum, using a method similar to that detailed in Chapter 3, has been reported, with no observed reduction in viability after 5 yr storage (5). This technique has been adopted by a small number of researchers to preserve selected cyanobacterial strains.