P>The exploration of new source materials and the use of alternative isolation and identification methods have led to rapid expansion in the knowledge of diversity; in Lysobacter, 11 new species having been described since 2005, and in Stenotrophomonas with six new species since 2000. The new species of Lysobacter, isolated by dilution and direct plating on standard media, differ in several key phenotypic properties from those obtained by enrichment on complex polysaccharides in the original description of the genus. Revision of the definition of the genus will be required. Both culture-dependent and culture-independent methods to assess community structure, in a variety of host and nonhost environments, have established that some species of Lysobacter are a dominant component of the microflora, where previously their presence had not been suspected. Culture-independent studies have generally not added new information on the occurrence and distribution of Stenotrophomonas maltophilia and other members of the genus, which are readily isolated on standard media from source materials. Lysobacter enzymogenes and Sten. maltophilia produce similar antibiotics and share some enzyme activities which, subject to safety considerations, may make them attractive candidates for use in biological control of plant diseases and of nematodes.