Since the epidemic began in the early 1980s it is estimated that over thirty million people worldwide have died from AIDS (the illness caused by the HIV virus). Around the same number are currently living with the disease and two million more people a year are becoming infected with it. Over three hundred million cases of malaria occur each year worldwide, with around one million people a year dying of it. More than three million people a year worldwide get cholera with around one hundred thousand people dying from it per year. Worldwide, more than one million people a year die of tuberculosis (TB) and around ten million people a year become newly infected with it. More than sixty thousand people worldwide suffer from cystic fibrosis. People with the disease on average, tend to die before they reach forty years old, sadly. This book is about explaining what causes these diseases and what cures or treatments are available. As they represent different types of disease in each case; I believe someone reading this will gain the understanding of not only AIDS, malaria, cholera, TB and cystic fibrosis; but also many other diseases that have the same or similar basis. This book will particularly benefit students of biology and medicine; but is written in understandable language for non-students; who may just have an interest in these diseases. I hope that by reading this book you gain an insight into the fascinating subject of the biology of these illnesses and that what you learn will benefit you and others around you.