The year 2007 commemorates the 50th anniversary of the publication of The Microbial World, the seminal microbiology textbook that shattered the microbiology world and whose first edition was coauthored by Roger Y. Stanier, Michael Doudoroff and Edward A. Adelberg. The year 2007 marks also twenty-five years of Stanier's passing away. The Spanish Society for Microbiology (SEM) with the support of Fundación Ramón Areces has organized a Symposium, in the frame of the 21st national congress of the SEM (Seville, 17-20 September 2007), to commemorate those anniversaries, and has invited us (Schaechter, Ingraham and Neidhardt) to contribute to this celebration.