Infectious diseases, also known as transmissible diseases, are the illness caused by an infection. The invasion of an organism's body tissue by the biological pathogens such as viruses, bacteria, fungi, parasites, prions and anthropods causes infections. These pathogens enter the body of an organism and start multiplying. The immune system of the host tissues fights against them. The infections that show symptoms are categorized as clinical and the infections that do not show any apparent symptoms are known as subclinical infections. The symptoms of infectious diseases vary from one disease to another but the most common of them include fatigue, weight loss, fever, running nose, coughing, skin rashes, loss of appetite, night sweats, chills and body aches. The medications commonly used to treat the infectious diseases are antibiotics, antifungals, antiprotozoals, antivirals and antihelminthics. This book presents researches and studies performed by experts across the globe. It contains some path-breaking studies in the field of infectious diseases. It will provide comprehensive knowledge to the readers.