Every year, between 4 and 20 percent of the world population catches some form of influenza. Influenza, or the flu, is an infection caused by a viruses, much like the common cold, but unlike the common cold, the flu, whether seasonal, avian, or swine, has killed millions around the world throughout recorded history. Advances in science are producing effective vaccines and medications to combat this disease, but the influenza virus continues to change. Readers will learn what the flu is and what it is not, what different types of flu exist, how to avoid infection, and what to do if they get the flu.