This text book is designed for molecular and structural biology of Aeromonas hydrophila. A. hydrophila is a bacterial pathogen which is associated with tail and skin rot, hemorrhagic septicaemia diseases in fish, amphibians and reptiles while meningitis and diarrhoea in human. A number of putative virulence proteins encoding and conserved genes are present in the genome of A. hydrophila which have been targeted by PCR for molecular diagnostics. It covers all potential techniques for identification, genotyping, cloning, expression, crystallization and also bioinformatics analysis for development of immunoassay, vaccines and other biotechnological applications. It helps in better understanding of pathogenesis and also useful in the development of effective vaccines and drugs for controlling the diseases. This book is recommended for use as a self-learning guide for students, scientists and researchers who deal the molecular and structural biology.