This book has been written for the diagnosis as well as the treatment of some important diseases of domestic and commercial birds. The language is very easy for the understanding of the major aspects of symptoms, diagonosis, disease prevention, control and treatment. This is the first version of the book especially designed for the veterinary students and the progressive farmers. In short, the book is the detailed description of different types of the diseases, causative agents for them, prevention and major aspects of biosecurity against theses diseases. The author of the book will be pleased to be informed for the correction of the errors if present.