When antibiotics were first discovered in the middle of the twentieth century, it seemed that they would be the answer to people's long struggle against infectious diseases. But over time, pathogens such as disease-causing viruses and bacteria have evolved so that they outsmart the drugs that are supposed to destroy them. Now, many of the medicines that people count on to make them better no longer work. Author Kowalski explains how this happened, the problems it causes worldwide, and what scientists think might be done to overcome the problem.