Earth is home to trillions of germs. But for most of human history, people didn't know germs existed! Healers of the past had different ideas about illnesses and their cures. They blamed illnesses on other causes and sometimes tried dangerous treatments. The invention of tools such as the microscope changed everything, allowing doctors and scientists to see germs and study their effects. This vivid graphic history profiles the people who helped discover germs. Discover the ongoing breakthroughs in research—and germs' surprising benefits for safety and sustainable energy.