Traditionally, the ex situ study of prokaryotes (members of Archaea and Bacteria) has required access to living cultures. Although it may be possible to maintain a small number of strains by serial transfer, such methods are not the best, particularly for long-term storage or for keeping a large collection. One of the major problems is dealing with the vast range of organisms that have been isolated to date. Particularly in the case of methods of cultivating prokaryotes, it is almost impossible to give a simple list of media to use. However, general principles are outlined that should cover most of the currently known prokaryotes in pure culture. The methodologies used for the long-term storage of prokaryotes may be divided into those that involve freezing and those that involve vacuum-drying. The methods described are those that are either used in the Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH (http://www.dsmz.de/index.htm) or in other national culture collections.