The object of this article is to draw attention to the significance of microbial diversity as a major resource for biotechnological products and processes. The topic is approached from two complementary standpoints. First, an attempt is made to assess the extent of biodiversity, particularly microbial diversity. In this context, the application of the modern techniques of molecular biology is enabling the detection of hitherto completely unknown groups of microbes and, also, is revealing the extent of genetic diversity within microbial taxa. The case is made for the establishment of sound microbial taxonomies both on the basis of satisfying fundamental scientific needs, and for designing effective isolation strategies. The impact of an ecological approach to search and discovery of novel organisms and properties also is emphasized and illustrated. Second, the question of screening a collection of appropriate microorganisms for the desired attributes is considered. The focus here is placed on modern intelligent or targeted screening, and on the power of molecular biology to extend the range of screening options. Discussions of microbial ecology or diversity only rarely touch upon questions of gene pool conservation. The point made here is that loss of biodiversity should be as ominous for microbiologists and biotechnologists as it is to conservationists. The article concludes with thoughts on some means of conserving microbial diversity.