Poultry is retained world-wide for various rationales. They can be maintained by masses including commercial farmers for meat and eggs, small farmers, and even by the families in the backyard. They are one of the economical sources of meat. Despite its role in elevating emoluments and trimming poverty in the developing countries, its production is curbed by vast range of constraints, including diseases. Poultry is affected by four main types of diseases: metabolic and nutritional diseases, infectious diseases, parasitic diseases, and behavioral diseases.Poultry production can be made victorious by taking preventive measures to eradicate the diseases. Key step for the poultry men is to understand rigorously the basis of the disease(s) to which domestic birds are susceptible to. Many scientists are allocating their time to study the diseases among poultry and to understand the factors contributing to the disease. As an editor, my aim is to elaborate the scientific side of the subject. In this book, efforts have been done to combine a vast range of published research studies on diseases among poultry.An infectious disease is a disease induced by seizure of a host by a pathogen which eventually multiplies in the body. Infectious diseases are often transmittable. These include Avian Encephalomyelitis, Avian Influenza, Candidiasis, Colibacillosis, Salmonellosis, Fowl Pox, Infectious Bronchitis, Marek's disease, Mycoplasmosis, Necrotic Enteritis, Newcastle disease, etc. These diseases are described in first 12 Chapters of this book. Metabolic and nutritional diseases are conditions caused by a deficiency or a disturbance of metabolic functions through insufficient nutrition. These include Wooden breast disorder, Leg disorders and so on. These diseases are discussed in the following two Chapters. A parasitic disease is caused by invasion of parasitic organisms. These include Coccidiosis, Cryptosporidiosis, Histomoniasis, Toxoplasmosis etc. These diseases are reported in Chapters 15-18. Abnormal behavioral patterns of the birds can lead to behavioral diseases. This is reported in the last Chapter of the book.I hope that this book will be beneficial for students, researchers, teachers, and poultry men. It will help in recognising the fact that the disease cannot be controlled by mere disinfection and treatment of ill birds, but involves many important matters such as the selection of flock, smart feeding, proper housing and environment, and successful management.