This book is II part of Fundamentals of Medical Microbiology Volume I.In this book we will discuss about parasite host relationship, methods of identification of bacteria,immunity etc. As we discuss in part I, Medical Microbiology is the study of the causes and management of infectious diseases. These can be caused by viruses, bacteria, micro fungi and protozoa. Medical Microbiology may overlap with parasitology,generally considered to be the study of diseases caused by multicellular parasites.The classification and identification of organisms are two separate but inter-related processes. Classification involves the identification of groups of organism that share common properties and that differ from other groups. Identification entails the assignation of an unknown organism to a group within a scheme of classification. For more than a century bacteria have been classified according to their "Gram reaction" - named after Christian Gram who devised the protocol for his staining process in 1884. This book have complete course for bachelor of medicine and surgery (MBBS)students,all chapters prepared according to MBBS syllabus