The Book describes fungi, bacteria and viruses (as well as subviral pathogens) in, light of recent information. It introduces the three domains (=super kingdoms), the Archaea, Bacteria and Eukarya, proposed by Carl Woese, and the new Kingdoms of Protozoa, Chromista and Straminopila. The new classification of Fungi (Kirk et al. 2001), bacteria (Bergey's Manual of Systematic Bacteriology, 2004) and viruses (International Committee on Taxonomy of Viruses, 2006) have been included. There are descriptions of Viroids, Virusoids, Virnos, and Prions Organisms before which viruses pale into insignificance in smallness of their size and ingenuity of parasitism. There is a separate chapter on Aids and HIV. I am sure students will appreciate these derive much value by the newer information about these organisms.