This book presents the knowledge in organized and simplified manner for gaining a deep insight into the subject and to understand its complexities. Microbiology is the specialized and dynamic discipline of biology related to study of micro-organisms includes bacteria, viruses, protozoa and fungi. These micro-organisms are ubiquitous and are in close relation to human beings i.e. shows their beneficial and detrimental effects. These are classified in two groups named Prokaryotes and Eukaryotes. Bacteria are grouped under prokaryotes, simplest, smallest and best studied micro-organism. Whereas fungi are eukaryotes. These may be pathogenic or non pathogenic. Disease caused by fungi is known as Mycoses. As these micro-organisms are dominant form of life on this planet so application of various chemicals and physical agents is required to get rid of them. The characterization of bacteria can be done by Gram staining where Gram positive cell wall stain purple and Gram negative will appear as pink in colour. An empirical choice of antibiotics and culture media is made on the basis of Gram’s report. Number of other diagnostic tests and staining are known and mentioned in this book.